Your answer would be that the appositive phrase is "the book by E.B White" and the noun renamed is "Charlotte's Web".
Explanation:
An appositive is a noun or noun phrase that renames another noun right beside it. In this case, the appositive phrase, "the book by E.B. White", renames the noun "Charlotte's Web". As this appositive phrase is nonessential, it is separated from the rest of the sentence with commas. This means that if it was removed, the meaning of the sentence would be left unchanged (see 1).
