Writer of examination for dog (6)
I believe the answer is:
setter
I believe this is a double definition.
'writer of examination' is the first definition.
(person who set the exam)
'dog' is the second definition.
(setter is a type of dog)
'for' is the link.
(Other definitions for setter that I've seen before include "who is giving you problems right now?" , "Long-haired dog breed" , "Puzzle composer" , "Thematic type [DOG]" , "pointer" .)