I believe the better approach to #1 is to: - say that you’re not sure - articulate an hypothesis of what it might be to the best of your knowledge (it's likely you’re going to be 80% right) - propose to launch an effort / work stream / project to figure it out In many cases managers are just happy with an 80% answer and will reject to waste efforts to dive deeper. Managers can deal with uncertainty and with situation…
Please don't do this. Many managers and clients have a far better bullshit detector than you give them credit for. They might never say it directly to you, but you just lost their respect by trying to guess instead of being honest. When programmers I interview try to bullshit their way through an answer they clearly don't know, it's almost always the end of the interview. Especially because I make it super clear at the beginning that I prefer "I don't know". A solid "I don't know but I do know I can get you an answer or an update in a couple of hours" is the approach that earns my respect every time. And likely you'll be right 100% of the time with that answer.