Put on film about essential sailor's workwear (6,6)
I believe the answer is:
donkey jacket
'workwear' is the definition.
'put on film about essential sailor's' is the wordplay.
'put on film' becomes 'donet' (I am not sure about this - if you are sure you should believe this answer much more).
'about' is an insertion indicator.
'essential' becomes 'key' (I've seen this before).
'sailor' becomes 'jack' (I've seen this before).
'key'+'jack'='keyjack'
'donet' going around 'keyjack' is 'DONKEY-JACKET'.
(Another definition for donkey jacket that I've seen is " Garment associated with building workers".)