The most common and most likely answer to this crossword clue is the 8 plus 4 letter word QUESTION MARK
I've seen this crossword clue in The Daily Telegraph
Q
U
E
S
T
I
O
N
M
A
R
K
More clues leading to the result QUESTION MARK
- Doubt the Gospel?
- Is Monet misrepresented in tiny but fundamental matter?
- ‘Quakerism’ … not ‘quaking’ … ?
- Cast doubt upon gospel?
- , 25. Ask a gospeller?
- Search in gospel to protect love — what’s that ?
- Cast doubt on earliest gospel? What is the point?
- Suggest the gospel isn’t truth? I’ve just written it!
- Expression of uncertainty using odd quotes in religious book
- Challenge once ready in Germany?
Buddy explains!

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.
What does QUESTION MARK mean?
QUESTION MARK noun- The punctuation mark "?", used at the end of a sentence to indicate a question.
- A state of doubt or uncertainty.
- An enigmatic, inscrutable, or mysterious person or thing; an enigma, a riddle.
- Polygonia interrogationis, a North American nymphalid butterfly with a silver mark on the underside of its hindwing resembling a question mark (sense 1).