What should I do to become a social worker in California?

The council on social work (cswe.org) has a program to evaluate foreign degrees you may want to look at this. Also your best bet is to start going to meeting for groups related to DV and get involved in this community. It is quite tight knit and they will know of job openings. Because DV is so grroots you ususually will not need a licence to get actively involved.