I don't know

Someone said that most atheists "avoid answering" questions about how we exist by saying I don't know.

Clearly if those people don't know the answer to that, or indeed any question, the only honest answer is I don't know.

When this was explained the person responded that it isn't honest, giving an example of in a courtroom if a judge asked you a question you could answer truthfully or say I don't know. You could not know, or you could be lying, therefore there is no truth.

He then said that "I don't know" cannot be verified, therefore there is no truth to the claim.

To try to illustrate the logic a couple of questions were asked of him: "what age am I?" and "Are there an odd or even number of stars in the universe?". For the first any answer other than "I don't know" (this exchange being the sum of all interaction between the two) would be a guess, and regardless of anyone's attempt to verify. For the second it is clearly one of odd or even, but nobody could possibly verify the answer.

The initial response was to simply ignore the questions. After being pressed to answer the response was that these questions are irrelevant and are just an attempt to change the subject.

How many logical fallacies did this person commit and what were they? I can think of a few but I'd like to see what others think.

...most atheists "avoid answering" questions about how we exist by saying I don't know.

Amazing Familiarity. Once can't possibly know this unless they have access to the minds of at least more than half of all atheists.

You then (correctly) used the Reductio ad Absurdum technique to demonstrate that saying "I don't know" is the best response to questions where you don't know the answer.

...giving an example of in a courtroom if a judge asked you a question you could answer truthfully or say I don't know.

False Dichotomy. "I don't know" could be the truth.

You could not know, or you could be lying, therefore there is no truth.

Non Sequitur. It does not follow that there is no truth because one could not know or could be lying.

"I don't know" cannot be verified, therefore there is no truth to the claim.

This is simply factually incorrect. The general assertion is if a claim cannot be verified, then there is no truth to the claim. The fact is, if a claim cannot be verified, we cannot make a judgement on the truth of the claim. This can also be an argument from ignorance - the person is saying because we cannot know if the claim is true, then there must not be any truth to it.

I fear that responses here will attempt to support positions on religion rather than objectively look at the fallacies. If you have strong leanings one way or another, and responding to this question, I ask that you please just focus on the fallacies. Thank you!

Could be an Appeal to Dunning-Kruger (cognitive bias). Haha!