Well... I had the "Question That Can Never Be Asked" right on the tip of my tongue, but couldn't pull it in. I had to go with what I had.
“On the fields of Trensalore, at the fall of the 11th, when no living creature can speak falsely or fail to answer, a question will be asked. A question that must never, ever be answered........The first question. The oldest question in the universe, hidden in plain sight.”
A clue.