Everything in exhibition is superficial (7)
I believe the answer is:
shallow
'superficial' is the definition.
('shallow' can be similar in meaning to 'superficial')
'everything in exhibition' is the wordplay.
'everything' becomes 'all' (I've seen this before).
'in' is an insertion indicator.
'exhibition' becomes 'show' (I've seen this before).
'all' placed within 'show' is 'SHALLOW'.
'is' is the link.
(Other definitions for shallow that I've seen before include "Frivolous" , "justice" , "Not profound" , "Superficial" , "Of waters, not deep" .)