* iarraidh: This is a general word for "ask" or "request." It's a good all-purpose option.
* faighnich: This is often used for asking a question.
* cuir ceist: This literally means "put a question" and is a more formal way of asking.
The best translation will depend on *what* you're asking. For example:
* "Ask him a question" - Faighnich ceist dha.
* "Ask for help" - Iarraidh cuideachadh.
* "Ask permission" - Iarraidh cead.
So, while iarraidh is a good starting point, providing the full sentence will allow for a more accurate translation.