Demand to see everything (4)
I believe the answer is:
call
'demand' is the definition.
(call is a kind of demand)
'see everything' is the wordplay.
'see' becomes 'C' (the word for the letter, according to Chambers).
'everything' becomes 'all' (all things).
'c'+'all'='CALL'
'to' acts as a link.
(Other definitions for call that I've seen before include "Ring or visit" , "Name; visit" , "Shout; ring" , "Be in control" , "Ring; name" .)