Answer:
The musician bowed and picked up his instrument, a violin.
Explanation:
An appositive is a noun or noun phrase placed next to another noun to identify or explain it. It can be placed before or after the noun it refers to, although it's more often placed after it. In this case, it's usually framed by commas.
In the given sentence, the appositive is a violin. It refers to the noun instrument and identifies it. As we can see, it's located after it and separated from it by a comma.
