One to whom a right is legally transferred (8)
I believe the answer is:
assignee
'one to whom a right is legally transferred' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for assignee that I've seen before include "beneficiary" , "Property is transferred to him" , "One to whom legal right is transferred" , "One receiving property" , "One to whom a right is legally transferred" .)