Was unable to pass on what one had learned (6)
I believe the answer is:
failed
'learned' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I can't see?
'was unable to pass on what one had' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'had' could be 'led' (leading is a kind of having) and 'led' is located in the answer.
The remaining letters 'fa' 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 failed that I've seen before include "Didn't make it - not well" , "Was unsuccessful, did not pass exam" , "Did not succeed, perhaps at exam" , "Didn't succeed" , "Bankrupt" .)