Knuckle down to, but find you can get no further with (3,5,2)

'knuckle down' is the definition.
Both the answer and definition are verbs in their base form.
Maybe there's an association between them I don't understand?

'but find you can get no further with' is the wordplay.
I cannot quite understand how this works, but
'find' could be 'get' (synonyms) and 'get' is found in the answer.
'you' could be 'u' (homophones) and 'u' is located in the answer.
'no' could be 'n' (common abbreviation) and 'n' is present in the answer.
This may be the basis of the clue (or it may be nonsense).

'to' acts as a link.

Can you help me to learn more?