Your question is Handling Unknown Client Questions. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Tell me about a time a client asked you a technical question and you did not know the answer in the moment. How did you respond, how did you find the answer, and what did you do afterward to make sure the same gap was handled better next time?