Pick up knight after king (5)
I believe the answer is:
learn
'pick up' is the definition.
('learn' can be a synonym of 'pick up')
'knight after king' is the wordplay.
'knight' becomes 'n' (chess).
'after' means one lot of letters go next to another.
'king' becomes 'lear' (I've seen this before).
'n' put after 'lear' is 'LEARN'.
(Other definitions for learn that I've seen before include "Read up on" , "Master" , "Acquire 28 across" , "Find out - assimilate facts" , "Absorb as knowledge, from book or experience" .)