If you’re asked a question to which you don’t know the answer in a job interview DO NOT start talking. Pause & ask for a moment to think about it. No one will ever say no and any employer who does/thinks less of you for asking is not an employer you want to work for.

Importantly, use the time to actually think of an answer

Best advice I got on defending my dissertation was to pause after every question, even if I knew the answer, so that when I didn’t know the answer, I’d have time to think without looking like I was trying to buy time.