Legal Question in Family Law in California

Depends on why you need to know. If it's part of litigation you can use discovery to find out. If you are, say, a doctor or a bank or escrow company being asked to follow the instructions of someone who claims to hold powers under an AMD or POA, you can demand proof. But in the absence of litigation or someone trying to exercise powers under such a document, no one has a right to know unless the grantor or holder of the power wants to tell you.