Some of the most common unanswered questions are:
How did everything start?
What was there before?
How was something made from nothing?
What came first, the chicken or the egg?
This video brought some great comments that are worth checking out, like this one:
Luke Jamieson: Here is my two cents: Space and time were created by something outside of space and time. The answer to the question “what created God” is that nothing created God and God had no beginning because he is outside of time. It’s impossible for us to comprehend similar to the way we can’t imagine other dimensions. People don’t usually address the fact that time was created as well as matter. And that whatever created time is obviously not bound by it.