What is the appositive in this sentence, "The artist Verdicini created his art by throwing paint onto a wall" ?
The appositive is "The artist."
An appositive is a noun or noun phrase that clarifies or redefines another noun. The main noun of the sentence is Verdicini; qualifying him as an artist does not matter. (Take the appositive out and you'll see it still makes sense grammatically.
A phrase does not have to be bookended by commas to be an appositive.