You'll know when you've got it (9)
I believe the answer is:
erudition
'you'll' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
'know when you've got it' is the wordplay.
I cannot really understand how this works, but
'when' could be 'on' (I've seen this in other clues) and 'on' is found within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for erudition that I've seen before include "State of learning or culture" , "profound scholarly knowledge" , "Learnedness, scholarship" , "Knowledge, learning" , "Great knowledge" .)