Last time I entered USA, the border officer asked me a lot of questions. Some of them were quite personal and others were about my destination in the USA. For example, he asked me where I would stay. I knew the address and since it was a private host, he asked me if I know the profession of my host. I couldn't answer this question and the border officer seemed a little bit surprised about that.
So my question is: What questions should I be able to answer when I want to enter the USA?
One of the roles of the immigrations officials is to determine if you are wanting to enter the country for legitimate reasons, and for reasons that are within the rules of whatever class of visitor you are seeking to enter the country as (eg, a tourist, for business, for work, etc). They are also trying to determine if you are likely to leave within the time allowed for your visa type, and that you are not involved in any way in some form of crime - including smuggling drugs or human trafficking.
With very few exceptions, they can basically ask you any questions they want to in order to determine if that is the case. From my experience of having passed through US immigrations over 30 times over the past few years, they generally have a few basic questions that they will always ask ("what are you here to do", "how long do you plan to stay" type of thing), and then depending on the answers you give to those questions they will either accept your answer and let you in, or dig deeper into the details.
The fact that you might not be able to answer one or two questions completely isn't likely to be in itself a problem, as long as they are convinced that you're entering for legitimate reasons. Not knowing the profession of your host would be expected if you were to say that you were doing a House Swap/found them on AirBNB/etc, however not being able to answer the same question would be very suspicious if you claimed they had been a friend for 20 years.
Other questions I've been asked over the years include everything from details on what attractions I was planning on seeing (when entering as a tourist), details on what I was going to learn (when entering for a training course/conference), details about the position I was applying for and where it was to be based (when entering for a job interview), and details about who I work for and what I do there (when entering on a work visa). I've also been asked if I have any relations in the US, details of where I'm staying whilst I'm here, flight details for leaving the US, and even where I had come from, and what I was doing there.
Even if you do have issues with the initial immigration officer you will not be immediately rejected for entry, but instead will be taken to a "secondary screening" area where they will re-ask many of the same question, and potentially do further research to determine if you are legitimate or not. eg, they might call you host and confirm that you are staying there and that the reason you don't know their profession is because you found them via AirBNB.
Just answer everything you can and be truthful about those you don't have answers to.
I usually can answer questions about where I'm staying, my travel dates and who I'm staying with etc (and always have all travel and hotel details printed out, to help make it easy for them to confirm if they want to - had them call up the hotel a couple of times!) but as I am often not sure about where I'm going I tend to just tell them roughly the sort of thing I'll be doing, eg:
A day spent seeing the Golden Gate and some wandering around tourist areas, then a couple of days with a friend up in San Rafael - not sure when, but here's his name and address, then 3 days at this conference
Your worst mistake would be to make up an answer or lie - partly because they are trained to spot lies, but partly because that forms a valid reason to refuse entry, so at that point they can cause you an awful lot of trouble.
When talking to a customs or immigration officer, the most important thing to do is tell the truth. This includes "I don't know" if that is the answer you have. The second most important thing to do is to show that you have planned and prepared, so that you trot out "I don't know" as little as possible. The questions start like this:
Everything else is to validate what you've said so far, or to decide about searching you and your luggage.
So, you say you're here for three weeks? Can you show me a ticket to go somewhere else 3 weeks from now? You say you won't be working but you'll be staying with your cousin or a friend? How well do you know this person? How likely is it that such a friend or relative would take you in and support you for this length of time? How likely is it that you might be planning to help that relative or "friend" in their business? Or that you will be doing some kind of work to support yourself while you're here? You say you're going sightseeing in Minnesota in January? What sights do you plan to see? You're here to ski? Say some ski-ing sentences to me so I can evaluate whether you've ever skied or not, and whether you really intend to.
I watch Border Security a lot. People show up and say they are visiting a cousin, who's a roofer, and it's totally a coincidence that they brought their tar-stained roofing clothes with them on this visit. They claim they are here for a few days of sightseeing, but can't name anything they plan to see, have no reservations anywhere, etc. Other times the stories seem ridiculous but a little checking by the border officers confirms them - the guys with $10,000 cash each and cashier's cheques for $30,000 really have negotiated to buy $40,000 trucks in Toronto and drive them back to California, saving $10,000 per truck. The guy here to visit his girlfriend with only $18 US cash and no return ticket really will be supported by her parents (who are waiting at baggage claim with a Welcome to Canada sign) while he trains with a Canadian football trainer in the hopes of returning to the States and cracking the NFL, and the parents confirm he won't stay too long. These people could have had a smoother process if they'd brought some paperwork or at least some names with them and been able to answer the questions right away. But the answers do come out in the end.
I've never experienced or heard of "skill testing" questions like what is the capital of something or who was the xth president. But I have never claimed to be a returning resident - I'm always a visitor. I have been asked surprisingly detailed questions that turned out to be motivated by the officer's curiosity. For example when visiting my book publisher, being asked about the next version of Windows or what Microsoft is going to do about [whatever] or which phone is the best phone to have. I don't think they're checking to see if I really am a technical author - they could confirm that on Amazon in a heartbeat. I think they sometimes are just interested in the people they meet and the stories they hear.
I've crossed the border hundreds of times (if not thousands), so they can basically ask you anything.
There's no reason to be nervous about the questions, unless you have something to hide. If that's the case, then do not attempt to enter the US lying otherwise you will be in a world of trouble.
I'm a US Citizen (naturalized) so my English is a bit broken, and I don't look American at all.
So as far as weird questions, I have been asked:
"Who was the 16th president of the United States?"
To which I answered "I don't know", so the officer triggered a "red flag" for them because apparently for him, every US citizen must know that the 16th president of the US was Abraham Lincoln. However, out of curiosity I asked him back (not recommended, though) if he know who the 44th president of the United States was, and he said he didn't know, that not all presidents are that important, and I said:
oh well.. the 44th is Barak Obama
When I used to cross the border a green card holder and even as a tourist, their questions were a bit "easier".
Questions that they have asked me before:
How long are you planning to stay?
Are you carrying more than $10,000 in cash with you?
Are you carrying any firearms, explosives, weapons, drugs, tobacco or alcohol with you?
Are you planning to commit any act of terrorism during your stay in the US?
How many times have you ever visited the United States?
How long did you stay during that time? Did you stay with the same person, or did you stay with another person? If you're staying with another person why you are not staying with that person again?
What do you do for a living in your country of origin? If you're a student what do you study? If you're working what stuff do you work on in your day-to-day?
What is the address you're arriving to?
As advised before do not lie, you can get in a world of trouble if you decide to lie and they catch you lying.
Their questions are driven by profiling needs: I was traveling from EU to USA alone, for leisure but for just five days... uncommon enough to raise some flag. When I explained that my purpose was to see my daughter who was an exchange student in the USA, the officer asked politely if I had with me, by any chance, a picture of me and her together. I had many in my phone, as you would expect. Hadn't I been able to show them to him, more questioning would have certainly been in order.
