Question: what is the answer to the riddle bilbo stumps gollum with?
Answer: Gollum tells Bilbo an easy riddle, and when Bilbo answers it, Gollum suggests that they have a competition: if Gollum can stump Bilbo, he eats Bilbo; if Bilbo can stump Gollum, Gollum will show Bilbo the way out of the cave.