Both. That depends on the context, and the sentence. 'I have a question for you'. 'I will direct this question to the audience'.

You ask a question TO somebody, but the question itself is FOR somebody. I will ask this question to the politician. I have a question for the politician.

"To" indicates who receives the direct object (DO) of the verb, i.e., the indirect object (IO). [Pattern: verb + DO + to + IO] - Tell your question to the teacher. - Repeat the question to the class. - Explain the question to him. - He announced the question to the participants. - I will say the question to you only once. While "for" can sometimes indicate the IO, it can also be used to indicate that the question is "on behalf of" someone or "for an intended purpose or reason." - He has a question for you. (IO, You are the intended recipient of the question.) - Repeat the question for the class. (IO, The class is the intended recipient of the question.) - Explain the question to her for me. (On my behalf; so that I do not have to explain.) - I asked the question for you. (On your behalf; so that you do not have to ask it.) - I asked the question for a reason. (I had a purpose.) Online resource: http://www.pearsonlongman.com/ae/azar/grammar_ex/message_board/archive/articles/00046.htm