Legal Question in Real Estate Law in California

You did not state where the truck is located. If the truck was taken by law enforcement and impounded you should get a copy of your marriage license and contact the agency holding the vehicle.

If it is being held by a private party, there is a legal action called "claim and delivery" or sometimes by its older name "replevin" by which one can demand the return of personal property. You would have to show a right to possession, which probably can be shown by the fact that you are (a) also a registered owner, or (b) married to the registered owner. Another possibility would be to contact the Department of Motor Vehicles for advice.