Crossword Genius

It normally completes the written enquiry (8,4)

Ross

I believe the answer is:

question mark

I'm a little stuck... Click here to teach me more about this clue!

'it normally completes the written' is the definition.
The definition suggests a singular noun which matches the answer.

'enquiry' is the wordplay.
I cannot really understand how this works, but
'enquiry' could be 'question' (synonyms) and 'question' is found in the answer.
The remaining letters 'mark' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

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

I've seen this clue in The Globe and Mail.
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