How do I go about getting a letter of testamentary and what judge do I go to, to have it signed?

The Window Clerk can not give you legal advice. I recommend instead that you book an appointment (or they also take walk ins) with Placer County self-help center. In order to do this you will need to go through security, enter the main Courthouse, go to the ticket kiosk and press the button to request an appointment with the legal self-help center.

Go to the customer service window. They will bw able to direct you more effectively.