What is the complete adjective clause in sentence She went to department where complaints are handled?

Here's why:

* Adjective clauses modify nouns (in this case, "department").

* "Where" introduces the clause and refers back to the noun it modifies ("department").

* "Complaints are handled" is the rest of the clause, providing more information about the "department."

The clause tells us what kind of department she went to—the one where complaints are handled.