This person's job or duty (6)
I believe the answer is:
impost
'duty' is the definition.
(impost is a kind of duty)
'this person's job' is the wordplay.
'this person's' becomes 'im' (this person means the crossword setter themselves).
'job' becomes 'post' (post is a kind of job).
'im'+'post'='IMPOST'
'or' is the link.
(Other definitions for impost that I've seen before include "Customs duty" , "A tax or duty levied" .)