One who’ll succeed in audition for show (3)
I believe the answer is:
air
'for show' is the definition.
(both can mean broadcast)
'one who'll succeed in audition' is the wordplay.
'one who'll succeed' becomes 'heir' (an heir is someone's successor).
'in audition' shows a homophone (sound like) (audition can mean hearing).
'heir' sounds like 'AIR'.
(Other definitions for air that I've seen before include "A number" , "that's inspired" , "It's a mixture mainly of oxygen and nitrogen" , "put on radio?" , "The earth's atmosphere" .)