You want to get from Hong Kong International Airport (HKG/VHHH) to West Kowloon High Speed Railway Station.
For the minimum number of transfers, your options are to:
- Take the MTR Airport Express (towards Hong Kong) to Kowloon Station, then a ~10min walk via a shopping mall and covered footbridge. The rail journey time is 22 mins and a single fare is HK$100. All major cards (Visa, Mastercard, UnionPay) are accepted at the customer service centre or ticket machines in front of the station. You can also buy tickets online beforehand.
- Take the bus A22 (towards Lam Tin Station) to Austin Station, Jordan Road, then a ~5min walk via a covered footbridge with elevators. The bus journey time is 35-50mins and a single fare is HK$39. Cards (contactless only) are accepted on buses. You can also pay at the customer service centre before boarding the bus.
Now back to your general questions:
Does the public transportation system in Hong Kong accept a foreign credit card or debit card, or US dollars?
Things have gotten complicated in the past few years as Hong Kong is currently in the middle of a generational change in payment methods. As a general rule of thumb, in 2023 US dollars are not (and unlikely ever) accepted and cards (contactless) are accepted in some but not all transport modes (mainly buses, see this page and this page).
Getting an Octopus card remains the simplest way in 2023 as it still has universal coverage in Hong Kong. The card is a stored-value card that is accepted in all public transport modes, convenience stores, supermarkets, and most food outlets. Of course, if you only intend to make a single journey in Hong Kong, the deposit (or the HK$39 charge for the tourist version) may not be worth it.
The same question about the other transportation systems for cabs or Uber like services.
Taxis still generally operate on a cash (Hong Kong Dollar) basis. Some (but not the majority of) taxis take Octopus and Visa cards.
If you use Uber, which has acquired HKTaxi and can actually get you a licensed Taxi in Hong Kong, you can pay in the app with your card.
Are there ATMs conveniently available for me to withdraw cash in either US or HK dollars, and then purchase fares?
Many ATMs in the airport give Hong Kong dollars (e.g. Bank of China (HK), citibank, HSBC, all unaffiliated). Some also give US dollars if I recall correctly (e.g. Travelex, unaffiliated), but as mentioned above, they are not accepted for public transport fares in Hong Kong.
This community generally recommends one use their ATM/debit card(s) to withdraw local currency. This is because credit cards generally attracts a cash advance fee in addition to the foreign transaction fee, and currency exchanges generally charges customers a large fee (outright or via a large currency spread).