Square knot I’m to unravel? (8,4)

I believe the answer is:

question mark

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'square knot i'm to unravel?' is the definition.
I can't tell whether this definition defines the answer.

'square knot i'm to unravel?' is the wordplay.
'to unravel?' is an anagram indicator (I've seen 'to unravel' mean this).
'square'+'knot'+'im'='squareknotim'
'squareknotim' anagrammed gives 'QUESTION-MARK'.

Can you help me to learn more?

(Other definitions for question mark that I've seen before include "Query" , "What ends this" , "Expression of uncertainty" , "Not believe the gospel" .)

I've seen this clue in The Times and The Sunday Times.

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