Some of my favorite things my family would bring back from the market when I was a kid were roast pig and roast duck. They are usually best eaten the day of, as reheating the next day can be tricky. Whatever you do, do not microwave it! Its makes the crispy skin soggy and the flavor becomes over cooked. Instead, one of best way to reheat it is to use stove top.
Reheating on a pan:
Heating the pan on medium heat (you can add a little bit of oil if you like, but you won’t need that much because the skin is already fatty).
Lay each piece, skin side down, on the hot pan and let it sit for about 5-7 minutes or until the skin becomes crisp and golden. Once its nice and crispy, each piece over and heat the other side. For a few minutes until it heated through.