Seek information in capacity of king (3)
I believe the answer is:
ask
'seek information' is the definition.
(I've seen this in another clue)
'capacity of king' is the wordplay.
'capacity of' becomes 'as' (I can't explain this - if you can you should believe this answer much more).
'king' becomes 'K' (abbreviation for king in chess).
'as'+'k'='ASK'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for ask that I've seen before include "Something demanded" , "Request, invite" , "Enquire" , "Seek an answer" , "Make enquiry" .)