In a large bowl, combine the pork, scallions, soy sauce, sesame oil and gingerroot. Mix well so that the flavors will penetrate the meat. Then add the cabbage and mix until all the ingredients are thoroughly combined. The filling will not taste right if you try to combine all the ingredients at once. Place 1 dumpling wrapper on a plate or a board. Place 1 scant tablespoon of pork mixture in the center. Moisten the edges of the wrapper with a little water, then fold them over the filling to form a half-moon shape. Pinch the center together first, then stand the dumpling up on its base and pleat one of the sides of the half-moon twice, halfway between the outer edge and the center. Pleat the other side in the same way and leave the dumpling standing up. Stand the finished dumplings on a baking sheet lined with wax paper. Do not allow the sides of the dumplings to touch each other, or they will stick together. Repeat, using the remaining dumpling wrappers and pork filling. The dumplings can be made in advance and frozen for up to 3 months, or they may be cooked immediately, either boiled or pan-fried. Serve hot, with Soy-Ginger Sauce on the side.
Combine all the ingredients in a small bowl. Mix thoroughly and serve. This sauce will keep for up to a week in the refrigerator, without the gingerroot. Add the gingerroot when ready to serve.
*If you cannot get napa cabbage, substitute green cabbage. Because it is not as moist as the Chinese cabbage, add 2 tablespoons of water to the pork filling before incorporating the cabbage.