Car Loan

What is the name of your state? CA

My sailor son and wife have separated. She took a car loan out under his name (using power of attorney) when he was overseas. His name alone appears as the debtor. The car is registered in both names although she has possession. He has been making the car and insurance payments. My questions are:

1) how can he get her name off the reigstration so that he can take the car and sell it or 2) even though the loan is in his name alone, does she have any responsiibilty for payment?

Many thanks in advance for your reply.