How much do you know? One of my strongest things as somebody who's looked to as a person who knows a lot, is that I will immediately go to 'I don't know' when asked that sort of question. I don't even make an additional promise, I just stop at 'I don't know'.

With your emphasis on 'confidently', it sounds like you're looking at social consequences. I find that stopping the conversation with 'I don't know' and getting on with what I'm doing, socially 'reads' as authoritative. I'm sure part of it is my lack of equivocation: if I went 'I'll get back to you, I promise I swear I'll be able to know eventually, soon, I promise, pinky swear I will honest!' there would obviously be no authority, I'd be grovelling.

I could probably double down, unethically. 'I don't know, what a stupid question, why would you even ask that malformed question, that's not a real question'. I think that would lead to suspicion, though.

'I don't know' can be a power move, if you HAVE the confidence to mean it and let it lie there. I guess that's the answer. "I don't know. This is what I'm actively doing now…" This relies very much on there being many things you do know…