It's not about being able to answer the question correctly, it's about having the gut to try and use your current knowledge of said topic to make some progress (even if wrong).
He will help guide you through if you get stuck - ideally you want to come across as someone who can be taught... so don't act stuck up, try to answer the question first... if it seems like you're not making progress or he seems to look at you weirdly (thus causing you to doubt your method/answer) then try another method... in the worst case, ask for a prompt.