The most common and most likely answer to this crossword clue is the 8 letter word GRILLING
I've seen this crossword clue in The Guardian
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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 = grilling.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 GRILLING mean?
GRILLING verb- To cook (food) on a grill; to barbecue.
- To cook food under the element of a stove or only under the top element of an oven – broil, salamander.
- To interrogate; to question aggressively or harshly.
- To feel very hot; to swelter.
- To stamp or mark with a grill.
- To make angry; provoke; incite.
- To terrify; make tremble.
- To tremble; shiver.
- To snarl; snap.
- A thorough interrogation.
- The act or process of grilling, or broiling.