If you are asked a technical question in an interview and you don't know the answer. What do you do?

Instead of trying to “wing it” and hope that you get the answer correct. The best thing you can say here is:

"I don't know, but this is how I would find out..." This is a sign of seniority for me.

It’s a lot worse if you get the answer wrong but you come out very confident believing it’s correct.

It’s impossible to know all of the things in software engineering. So not knowing something is no issue at all.

As long as you show that you can either find the answer or learn if you are given the time to do so.