What's the one question you would like to ask if the answer were guaranteed to be correct?
What happens after death?
I understand the body decomposition that happens, but this question is more about what happens to our consciousness, some would say soul. Is there life after death? Is it just a different plane of existence or is there a heaven and hell? Does our existence just stop and our atoms get reused in new combinations? If we continue on, in what form? Do we meet the people we knew in life? Do we have to answer for our choices?
There are just so many aspects of this question that I could go on for a very long time, but I won't.