Subject's art ultimately removed from far side of NY museum (5)
I believe the answer is:
theme
'subject's' is the definition.
('theme' can be a synonym of 'subject')
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for theme that I've seen before include "Musical motif" , "The main sound" , "Main idea or topic" , "Motif, topic" , "[(type of) PARK]" .)