how do you subpoena a third party?

[snow banana flake]

I need records showing how much alcohol was consumed at a bar by my ex. My daughter was there and we have a court order stating he may not drink, the bartender told me it was three beers but will not testify without permission from the owner and he said not without a subpoena but that if I get it he will give me the receipts and a video of my ex drinking. What papers do I need to file to do this? If it matters I live in California.
I am also aware that he was drinking at a bar and grill but I do not know what days, can I subpoena for all his credit card receipts?