Rigged Riddle

"Not fair! not fair! It isn't fair, my precious, is it, to ask us what it's got in it's nassty little pocketsess?"

- Gollum

A “riddle” that the person answering can not reasonably know the answer too, as it depends on information only the asker should know. Obviously the person asking the riddle tends to win.

Literature

 * In The Hobbit, Bilbo asked Gollum “What have I got in my pocket?” Understandably, Gollum asserts that this riddle isn't fair. Funny thing is Bilbo was talking to himself when he said this, but Golem interpreted it as part of their riddle game and it is only after Gollum protested that Bilbo deliberately used it as the riddle.

Oral Tradition, Folklore, Myths, Religion, and Legends
"What did Odin speak into Baldr’s ear before he was placed on the pyre?"
 * Odin did this a couple of times in Norse Mythology. On both occasions, he used the same question


 * In Hervarar saga ok Heiðreks (The Saga of Hervör and Heidrek) One time while Odin was disguised asked King Heidrek numerous riddles. In this contest, Odin was the only one asking riddles.
 * Odin asked this with Vafþrúðnir (mighty weaver) in the poem Vafþrúðnismál. In this contest Vafþrúðnir and Odin asked each other riddles.
 * In The Bible, one time Samson came across a lion corpse with honey inside and used that as the basis of the riddle.
 * What is Rumplestiltskin’s name?