A power of attorney is apostilled through the notary. You sign it in front of a California notary, and the Secretary of State then authenticates the notary’s signature.
Two things matter. Do not sign it in advance — the notary has to witness the signature. And check whether the destination country requires specific wording: Mexico, India, Spain, and the Philippines all commonly do, and several consulates supply their own template. A power of attorney rejected abroad has to be redone from scratch.