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” for which the person answering can not reasonably know the answer, 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 actually talking to himself when he said this, but Gollum 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

 * Odin did this a couple of times in Norse Mythology. On both occasions, he used the same question "What did Odin speak into Baldr’s ear before he was placed on the pyre?"
 * 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 a beehive filled with honey inside and used that as the basis of the riddle. Unlike some other examples, this sounded like a proper riddle, instead of a straightforward question with a secret answer.
 * What is Rumpelstiltskin’s name?