As a female traveler I will be in Thailand for around 2 months in mid November to have fun and complete my professional diving lessons. I would like to be familiar with Thai culture and foods and also it would be an opportunity to find female sex workers and know what they really feel and want. I have heard and read that many of them have chosen this as an ordinary job and do not feel that they are forced to do it and are happy about their lives. As a curious traveler who writes and searches and investigates for it I like to know more. I was thinking with myself it may cause a negative impact or maybe it is not acceptable or permitted in Thailand for a traveler to ask such questions and search about. If you are familiar with Thai law and culture it would be great to guide me about.
I've been on Thailand in January/13 for about 2 weeks passing through Bangkok, Koh Samui, Krabi, Phi Phi, Kanchanaburi, etc..
In Bangkok was where I saw more freedom of natives in talking about sex with tourists. In everywhere was someone offering to me to go to any of theirs sexland places (In Bangkok we can see an entire district with expertise in Sex Tourism including some bizarre things like Ping Pong show, etc).
So, this subject is broadly talked in Thailand and I think this will not be a problem to you. I only think you will need to pay for it. There is a chance of them to charge you for an "Interview" about their job.
A way to get this interview is to visit a sex house and search for one sex worker who looks sympathetic and allows you to interview her. I'm sure her will not mind in spend her time talking with you.
I hope this can be useful to you.
Thailand is generally a free country and, outside of talking negatively of the king, you are free to talk to anyone about pretty much anything.
This includes sex workers who are people too. While you and others may treat them as another tourist attraction, you can get to talk to them quite easily if you treat them like you would anyone else. People from Thailand are generally extremely friendly and talkative. They are often just as curious about you as you are about them.
The best advice if you want to approach a sex worker is to find where they are many of them and start talking when they are not busy. The truth is that there are so many of them in some areas that you will see dozens waiting a street corners just chatting with each other. They approach males mostly, so as a female you may have to get the conversation started. Just smile and talk to one who is not busy. Try not to make it sound like an interview and be polite.
There are many shades of sex workers in Thailand and you may find that what constitutes one does not coincide with how things are in other places.
As a male traveling alone in Thailand, whenever I'm in a bar, I'm approached by bar-girls hustling drinks. I don't like to send them away since every baht they don't earn from drinks is one they have to earn on their backs.
I usually buy the girl a "lady-drink", 30 or 40 baht for a shot of apple juice with just enough tequila in it to make it smell like liquor, and chat with her for a while. We usually end up talking about her kids -- every bar-girl I have ever met has at least one adorable moppet at home, usually two, and a phone full of pictures of them.
As for "permitted", I've never tried asking them about their work, but since they are fairly enthusiastically asking me to have sex with them, I don't think inquiries into their profession would be taken amiss.
In fact, one time, two bar-girls were working me (at a place that charged an unheard-of 100 baht a drink!) but after an hour hadn't propositioned me. I finally asked them if they were prostitutes. Once I explained what the word meant, they said they weren't -- they were "coyote girls", just dancers and drink-hustlers, but not hookers, a new phenomenon as far as I know -- but they didn't take the slightest offense and offered to find a prostitute for me (I declined).
I'm curious whether as a female alone, you would be approached, but I'm quite certain that if you offered to buy a bar-girl a drink, she'd be more than happy to talk to you. Or sleep with you, for that matter.