I agree that "what are you asking for?" should be accepted. The problem, as someone elucidated in another post, is that no context is provided. "Ask what?" could be a response to a command, but that question almost always starts with "And" -- the same goes for "Ask for what?" "Demander quoi?" feels like it's a initial interrogative sentence and not a response. I suppose that "For what are you asking?" should also be accepted, less someone has quibbles with ending a sentence in a preposition.