Question

sirius blacks vocal coach a part - time opera singer is usually very dramatic.

Explanation:

The sentence needs non-restrictive appositive punctuation to set off the extra descriptive information about the vocal coach. The phrase "a part-time opera singer" is additional, non-essential detail about Sirius Black's vocal coach, so it should be enclosed by commas.

Answer:

Sirius Black's vocal coach, a part-time opera singer, is usually very dramatic.