Jill is wearing earrings that have gold posts.

Identify the word modified by the underlined adjectivial clause...
that have gold posts is underlined...

Jill
is
wearing
earrings

earrings...sorry I was in a hurry

Right.

Let us know what YOU THINK, and we can go from there.

Thank goodness.... :)

The underlined adjectival clause "that have gold posts" modifies the noun "earrings." Adjectival clauses function as adjectives and provide more information about a noun in the sentence. In this case, the adjectival clause specifies the type of earrings Jill is wearing by describing that they have gold posts.