First ask him in person or by email "can I bring anything?"

Most likely, you get an answer, "You don't need to bring anything. Just show up." However, if you are a good cook (or if you've learned a nice party dish here), you can also reply back to say thank you and offer to bring a Chinese dish. Make sure it's just an appetizer or dessert, so you don't take over the main dish. You can make a vegetarian dish to be on the safe side or check with him first like "I would be happy to bring a cabbage pork pot sticker dish for appetizer, is that okay?" Do not offer to bring a pumpkin pie. Also, if you will just buy a dish from a supermarket, don't bother -- there is nothing special about it.