My kids ask a lot of questions, often at inopportune times (like when we're trying to get out of the house). And many of those questions I either can't answer at all, or could only give an incomplete, possibly wrong, answer.
Therefore, we keep a Question Box in our house. Anyone can write down a question and put it in the box. Periodically, usually during dinner, we'll open it up and pull out a few of the questions. Usually between me and my husband we'll be able to answer each question, at least partially, without a reference. Don't have time to answer? That's a question for the Question Box. Don't know the answer? That's a question for the Question Box. You get the idea.
We also play a game at restaurants that involves asking each other factual questions. We encourage the kids to try to stump the parents, which they often do. We ask the kids questions relating to what they've been learning about recently. Sometimes the answer is easy, sometimes we are stumped. The rules are: no opinion questions (what is your favorite color?), and the questioner has to know the answer (or at least be pretty certain). Since we usually play this at the local Mexican restaurant, an additional rule is that you can't eat a chip until you've answered your question (this prevents us from gobbling all the chips!)
This doesn't address the underlying problem between you and your son, but perhaps it can help. I never pretend to know all the answers, and neither does my husband (although he is much better at coming up with a response than I am). But I do love to find things out, look things up, and learn. I think it is much healthier to model learning and exploring, rather than model having complete knowledge of everything, which isn't possible.
