Come on stage as a nobleman, for the audition (6)
I believe the answer is:
appear
'come on stage' is the definition.
'appear' can be an answer for 'come' (I've seen this before). I'm not certain of the 'on stage' bit.
'a nobleman for the audition' is the wordplay.
'a nobleman for' becomes 'app' (I can't justify this - if you can you should give a lot more credence to this answer).
'the audition' becomes 'ear' (ear is a kind of audition).
'app'+'ear'='APPEAR'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for appear that I've seen before include "hove in sight" , "Come on the market" , "Seem - emerge" , "Become visible like ghost" , "Materialise like ghost" .)