So unable to answer with some certainty (2,8)

I believe the answer is:

no question

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

'answer with some certainty' is the definition.
The definition suggests a singular noun which matches the answer.

'so unable to' is the wordplay.
I cannot quite understand how this works, but
'unable to' could be 'no' (I've seen this in other clues) and 'no' is found within the answer.
The remaining letters 'question' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Guardian.

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