East Ender perhaps who aspires to appear on a musical show (5)
I believe the answer is:
opera
This clue could be a double definition.
'east ender perhaps who aspires to appear' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'a musical show' is the second definition.
'on' acts as a link.
(Other definitions for opera that I've seen before include "Lohengrin, say" , "Eg, Der Rosenkavalier" , "Musical works" , "The Magic Flute, say" , ""The Magic Flute", for example" .)