Trainer's work assignment could be regularly returned (8)
I believe the answer is:
educator
'trainer's' is the definition.
(I've seen this before)
'work assignment could be regularly returned' is the wordplay.
'work assignment' becomes 'rota' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'returned' says the letters should be written backwards.
'could'+'be'='couldbe'
The alternating letters of 'couldbe' are 'cude'.
'rota'+'cude'='rotacude'
'rotacude' backwards is 'EDUCATOR'.
Can you help me to learn more?
(Other definitions for educator that I've seen before include "Teacher, lecturer" , "Trainer, teacher" , "Instructor" , "school worker" , "master, say" .)