King looking at what typist is doing (6)
I believe the answer is:
keying
'what typist is doing' is the definition.
(keying can mean typing)
'king looking at' is the wordplay.
'king' becomes 'K' (abbreviation for king in chess).
'looking at' becomes 'eying' (to eye something is to look at it).
'k'+'eying'='KEYING'
(Other definitions for keying that I've seen before include "Tapping" , "harmonising" .)