Gaining knowledge (8)
I believe the answer is:
learning
'gaining knowledge' is the definition.
('learn' can be a synonym of 'gain knowledge')
This is the entire clue.
(Other definitions for learning that I've seen before include "Large inn (anag)" , "Instruction" , "A little of it is said to be a dangerous thing" , "Discovering, finding out" , "Cognitive process of acquiring skill or knowledge" .)