Discover king in play with knight (5)
I believe the answer is:
learn
'discover' is the definition.
(I know that discover is a more specific form of discover)
'king in play with knight' is the wordplay.
'king in play' becomes 'Lear' (Shakespeare's King Lear).
'with' is a charade indicator (letters next to each other).
'knight' becomes 'N' (chess abbreviation).
'lear'+'n'='LEARN'
(Other definitions for learn that I've seen before include "Ascertain" , "Gain knowledge or skills" , "Comprehend" , "Succeed in school" , "Be educated" .)