Final answer:
The bold appositive phrase 'Edna Krabappel' provides specific information about who 'your friend' is, and it's emphasized by the sentence structure.
Step-by-step explanation:
The bold appositive phrase in the sentence "I wonder if your friend Edna Krabappel has ever gone hang gliding" refers to "Edna Krabappel." An appositive is a noun or noun phrase that renames or provides additional information about the noun next to it. In this case, "Edna Krabappel" renames and specifies who "your friend" is. When using dashes, like in the given examples, the dash can help set off or emphasize an appositive that provides clarifying information that is considered important to the meaning of the sentence.