Please explain how to change this interrogative sentence into passive voice. Is he the musician for the evening?
Is he the musician for the evening?
It's not possible to change the sentence into the passive as the verb be (is) is a linking verb.
You don't form passive structures with linking verbs like be, seem, become where the complement of the verb refers back to the subject. You need a transitive verb, which has an object, to form the passive. For example:
They requested me (object) to be the musician for the evening (active).
I was requested (by them) to be the musician for the evening (passive).