The above response is essentially correct but, with due respect and in my opinion, is inadequate and therefore somewhat misdirected.
First, you will need to file an Application for Entry of Sister-State Judgment (EJ-105). You can find an online DIY form here:
http://www.courts.ca.gov/documents/ej105.pdf. It is not likely that anything is needed under 6(b).
With it, you will have to include a “certified” copy of the judgment. It’s not the same as a copy sent/given to you and may be referred to as an “authenicated” copy but will have to bear a court attestation (like a notary’s seal) that it is a true and correct copy of the original. Check with your court.
As you will see from EJ-105, if you want post-judgment interest, you will have to provide the statutory authority. For you, it is 9% per VA Code sect. 6.1-330.54 (unless the judgment was upon a contract providing for a different rate). Once the judgment is domesticated, it will earn interest at the CA rate of 10% post-judgment.
Pay the filing fee (based on the amount of your judgment – check with CA court/clerk where debtor resides/does business - recoverable cost as part of enforcement).
The CA court then issues a Notice of Entry of Sister-State Judgment (EJ-110)
http://www.courts.ca.gov/documents/ej110.pdf.
That must be served on the debtor. After service, the debtor has 30 days to contest the validity of the VA judgment (I’ve never seen that happen, much less successfully). The domesticated judgment then becomes final and can be enforced in all manner permitted by CA law, including a wage garnishment, but more goes beyond the scope of your question. There are attorneys, collection agencies and even some process servers who will handle all of this for you, but you’ll have to provide the judgment copy and sign EJ-105. Anything you do yourself should lessen the cost.
“If you are talking about a copy of the judgment, he should be able to get hold of that quite easily, if he hasn't already” has nothing to do with this process.