The most common and most likely answer to this crossword clue is the 10 letter word DISBELIEVE
I've seen this crossword clue in The Guardian
D
I
S
B
E
L
I
E
V
E
Buddy explains!

The straight part
We know that "Question" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case question = disbelieve.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
DISBELIEVE verb- To not believe; to exercise disbelief.
- To actively deny (a statement, opinion or perception).
- To cease to believe.