How to answer questions you don't have the answer for (yet)
The classic is "I will come back to you" and "I will answer you separately in an email later". But how do we go about it?
Anticipating the questions that could come can actually help you to answer the impossible questions before it is asked. For example, coming into an interview, you can anticipate there will be questions on your expected salary. To make an informed decision, utilize your network, ask people who are in similar positions, look for similar roles on job sites, check salary review reports... to find out a range that is comfortable to you to accept, and reasonable for companies to accept.
Whenever possible, ask for more information. Sometimes things will just solve themselves out by you asking one more question. Don't just accept what is given to you as it.
The outcome of meetings are solutions and next steps, so focus on what you can do, not what you don't know. I recently joined a meeting when we discuss a situation we have not faced as a team. Instead of focusing on what we don't have (experience with similar cases), I focus on what we can do to move forward, instead of not making any action, and therefore not making any progress.
One of my previous managers told me this, and I resonate with it more and more as time goes. You are not supposed to know everything, and sometimes people ask you things outside of your responsibility. The answer could be point them to the right people, or simply mention this is not under your scope to know.