Does he have to contact the child support agency or will the agency eventually locate his place of employment?

My husband owes backed child support from a previous marriage. The children are now in their twenties and he still owes the money which sucks. The IRS has already taken his refunds for child support and child support had took some wages from his previous places of employment. Now the DCSS in Calif has sent him a letter to provide info on where he works at now. BTW, I thought that they would track where he works at like they did before even without us knowing until his last job before the one he works now which is in the state of S.C. So if in any case he doesn't tell them where he works at now, will DCSS find out anyway and just garnish some of his wages like they have done previously or what will happen? thanks