I had an original order for child support in virginia and my ex wife relocated with my child to California. I have moved to Nevada with the Military. If I petition the court to reduce my child support because I have had another child and my ex wife is now employed will the court use California's cost of living in the formula?

What is your "home state" ?

When in the military you should have a home state and that's not always the one your living in. So if your career started in Virginia then for now that IS your home state.

The general rule is that jurisdiction remains with the original court as long as one of the parties remains within the jurisdiction. If your home state is still VA then jurisdiction may remain there.