When king gets singular demands (4)
I believe the answer is:
asks
'demands' is the definition.
('ask' can be a synonym of 'demand')
'when king gets singular' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'king' becomes 'K' (abbreviation for king in chess).
'gets' means one lot of letters go next to another.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'as'+'k'+'s'='ASKS'
(Other definitions for asks that I've seen before include "Poses a question" , "Makes an inquiry" , "Demands (something of someone)" , "Inquiries" , "Requests information about" .)