Everyone in performance on wobbly set is most superficial (10)
I believe the answer is:
'most superficial' is the definition.
(shallow can mean superficial or vain)
'everyone in performance on wobbly set' is the wordplay.
'everyone' becomes 'all' (I've seen this before).
'in' means one lot of letters goes inside another.
'performance' becomes 'show' (I've seen this in other clues).
'on' indicates putting letters inside.
'wobbly' indicates anagramming the letters (I've seen this in other clues).
'all' put into 'show' is 'shallow'.
'set' with letters rearranged gives 'est'.
'shallow' inserted inside 'est' is 'SHALLOWEST'.
'is' acts as a link.
(Another definition for shallowest that I've seen is "Extremely thin".)