Find out when? Sure (9)
I believe the answer is:
ascertain
'find out' is the definition.
(ascertaining is a kind of finding out)
'when? sure' is the wordplay.
'when?' becomes 'as'.
'sure' becomes 'certain' ('certain' can be a synonym of 'sure').
'as'+'certain'='ASCERTAIN'
(Other definitions for ascertain that I've seen before include "settle" , "Find out - make sure" , "Discover" , "Become aware" , "Prove" .)