If I pan fry battered oysters, when do I add beer and wine?

You should follow your recipe if you have one - for reference, I looked at these: 1, 2, 3.

One recipe specifies quickly poaching your oysters with ginger, spring onion, and a splash of cooking wine, this is an optional step but may remove some fishiness (or 腥味) from the oysters. Next, dredge your oysters in cornstarch (you could also use potato starch) and fry. The listed recipes all pan-fry but you could deep-fry.

The sauce/glaze: fry shallots/red onion with garlic, then add your port wine, some soy sauce, oyster sauce (could substitute hoisin), and sugar. Reduce the sauce then either pour it over your oysters to put them in the oven or toss them together in the pan. It looks like the restaurant does the latter. They may also blend the aromatics into the sauce then reduce it further, remove them after cooking, or just leave them out entirely. None of the recipes mention beer.