Copies rap by Oscar and Gordon Bennett (9)

I believe the answer is:

knockoffs

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

'copies' is the definition.
(I know this)

'rap by oscar and gordon bennett' is the wordplay.
I cannot quite understand how this works, but
'rap' could be 'knock' (synonyms) and 'knock' is located in the answer.
'by' could be 'of' and 'of' is found within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Independent.

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