Good Q, but "Known" can often be relative to "belief"
I majored in Philosophy,,,Gads No money in that,,,smiles.
Life according to what you believe is either,,,Real, or illusionary, and we often make the choice of what to question, or not, based on how we are experiencing either.
BTW,,, there are likely countless questions, not meant to be answered in ones lifetime, or plane of existence.
What grabbed me more however was your use of the word TRUTH.
"Truth" in its base form, is belief, faith, etc.... While "FACT" though often disputed,,, "IS" and stands no matter who believes in it. TRUTH comforts us,,,often,,,while FACT insists we challenge it, even when we "believe" things such as 1 plus 1 equal 2.
Rev. Steven