The most basic response when I don't know the answer to a question is to not say anything. If someone asks me a question and I don't know the answer, I don't speculate. I don't say anything. Now if someone asks me a question and they need an answer, I simply tell them I don't know. If I don't know, I will ask someone what should I have said. Maybe not so much what should I have said, but if you don't know the answer to a question, why speak? Go find someone who does know the answer to the question. That's what I would do.