can somone please highlight that makeup the appositive phrase The alien spaceship, a flying silver disk, hovered over Dory's school.

Highlight of the appositive phrase:

The alien spaceship, a flying silver disk, hovered over Dory's school.

Explanation:

We can highlight the appositive phrase in the above sentence as "a flying silver disk."  It renames the alien spaceship, which a noun phrase with another noun phrase in order to rename it, making it clearer for the audience or readers to understand the subject that hovered over Dory's school.  Appositive phrases normally add meaningful details to the nouns they describe.  They are usually separated by commas, depending on the sentence style.