Place to make a note of profit (6)
I believe the answer is:
margin
I believe this is a double definition.
'place to make a note' is the first definition.
(you might make notes in the margin of a page)
'profit' is the second definition.
(margin is a kind of profit)
'of' acts as a link.
(Other definitions for margin that I've seen before include "Bound" , "Boundary line or the area" , "Blank space around the edge" , "Permissible difference" , "Blank space around a page" .)