I've learned not to say I don't know. Every single time, I get told, "that's gawd. Mmhm. He takes keer of everthin."

I taught my students it was proper to say, "I don't know and I'll be sure to check." If I didn't know, I would ALWAYS look and come back and inform them - few really cared, but it proved my point.

I've learned a while ago that you are not required to attend every argument to which you are invited. As for direct questions, if I don't know, I say I don't know. If it's important to me, I'll make a note and follow up on it. Except for little white lies (no, no, those jeans look great on you), I don't give answers I know are not true.

I never admit I don't know....its always "I'll have to get back to you on that, .and I only lie when in dreadful fear for my life. .

Zero!

I tend to fiercely protect my own credibility, and I will always answer honestly with "I don't know" than lie to pretend I do. There is no shame in not being a know-it-all, and no shame in saying "I was wrong about that." It's far more important that people understand my sincerity.

“I don’t know anything. Ever. It’s really quite relaxing.”

My answer is l don't know how the universe got here. I don't know if there is a reason the universe exists or it just is. I do say there have been at least 2000 Gods or more that human beings have come up with and not one of those thousands of Gods is the answer because historians have traced the origins of those Gods and they have all been made up by men. There may be some unknown power we have yet to discover responsible for our existence, but l am sure it has nothing to do with the Gods humanity has conceived, which is why l go back and forth as to whether l am an Atheist or an Agnostic.

I don't know.

I don't know a lot of things and try not to lie about it.

I always start with. "I don't know." as the default, because in most cases I think that that is the most honest and accurate answer, and that it is that basic level of, honesty, which makes most of the sceptical ideologies better than theist ones.

I probably don't lie that often these days, since now that I am retired and post self employed, I chose not to mix with people I would feel the need to lie to, any longer.

Well speaking on a personal basis here, when it comes down to discussions/debates regarding religion and religious doctrines, etc, I can honestly state that I never need to say the words "I don't know" since I have made it my aim in life to discover everything possible regarding Christianity, its tenets and doctrines, its ACTUAL history, the bible and its TRUE origin, etc, etc.
And if a subject other than religion comes up and I'm unsure of the answer to a question, etc, THEN I make it a point to find out whatever it is that I need to know and to understand as well.

I say 'I don't know' all the time as an agnostic atheist, but I don't know how related to my beliefs about religion it is. I think it has more to do with my desire to not be wrong. If I don't know something, I either say I don't know when asked directly, or simply keep my mouth shut if I wasn't (no point in volunteering that you don't have anything to add).
As for how often I lie, I imagine pretty often, but rarely, if ever, in an attempt to be maliciously deceptive. Sam Harris makes a really good case for never lying about anything ever, but I just can't imagine it in practice. Unless you were famous for not lying, thereby providing anyone you come across foreknowledge that you wouldn't lie to them at all, the self-imposed inability to lie would definitely come off as a personality disorder or maybe autism.

Well, I don't know about agnostics (I dislike questions phrased like this) but as an atheist I am happy to say 'I don't know', since I have no problem acknowledging the limits of my knowledge. Your second question is asking how often we lie (let's not be coy). There are lies and then there are lies, like telling a salesperson in a shop that you'll think about buying some product when you know you won't.