I'm going to take a slightly opposite to view to Niknak's and say you shouldn't have to ask (at an ATC field).
If it's an ATC set-up you should be
told in good time before you've even said anything - believe it or not they often have a better idea than you where you'll be parking (As I've pointed out to the occasional visitor who THINKS he's parking one place when I KNOW he's parking in another
).