Green film about working for financial specialist (9)
I believe the answer is:
economist
'financial specialist' is the definition.
(I've seen this before)
'green film about working' is the wordplay.
'green' becomes 'eco' (abbreviation for ecological).
'film' becomes 'mist' (to film over is to mist or fog over).
'about' means one lot of letters goes inside another.
'working' becomes 'on' (on can mean working or activated).
'eco'+'mist'='ecomist'
'ecomist' going around 'on' is 'ECONOMIST'.
'for' is the link.
(Other definitions for economist that I've seen before include "Friedman, say" , "He studies money etc" , "One versed in the management of a country's material resources" , "Financial expert" , "Financial specialist" .)