Well, I suppose it depends on what 'questioning' means in the context it is being used, but overall if it is a non Christian questioning my beliefs in Christ I would try to use it as an opening to discuss and explain the what and why of them.
if it's presented in the form of a challenge to my beliefs I would first ask what they know about them, there is always the chance that they are trying to decide on which way they want to go for themselves and looking to you for information (often without them actually realizing that is what they are doing).
The hot and the cold are where the opportunities to carry the gospel lie, those who really don't care one way or the other aren't really open to considering anything other than what they are already comfortable with and usually aren't going to be found among those questioning our faith.