The most common and most likely answer to this crossword clue is the 13 letter word INTERROGATORY
I've seen this crossword clue in The Times
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More clues leading to the result INTERROGATORY
Buddy explains!

The straight part
We know that "Questioning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case questioning = interrogatory.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 INTERROGATORY mean?
INTERROGATORY noun- A formal question submitted to opposing party to answer, generally governed by court rule.
- A question; an interrogation.
- Serving to interrogate; questioning.