Find out king's name (5)
I believe the answer is:
learn
'find out' is the definition.
(I know that find out can be written as learn)
'king's name' is the wordplay.
'king' becomes 'lear' (King Lear).
'name' becomes 'n' (common abbreviation e.g. on forms).
'lear'+'n'='LEARN'
(Other definitions for learn that I've seen before include "Acquire 28 across" , "Acquire information" , "Read up on" , "Hear - memorise" , "Gain knowledge or skills" .)