General Synonyms:
* Inquiry
* Query
* Interrogation
* Problem
* Issue
* Doubt
* Puzzle
* Challenge
Formal Synonyms:
* Interrogatory
* Query
* Examination
* Inquisition
Informal Synonyms:
* Ask
* Wonder
* Request
* Demand
* Challenge
Other Synonyms:
* Conundrum (a confusing and difficult problem or question)
* Dilemma (a situation in which a difficult choice has to be made between two or more alternatives)
* Riddle (a question or statement intentionally phrased so as to require ingenuity in ascertaining its answer or meaning)
* Mystery (something that is unknown, puzzling, or unexplained)
The best synonym for "question" depends on the specific situation and the intended meaning.