To make the stock, combine everything but the gelatin in a medium pot, cover with water and bring to a simmer. Cook over low heat, without bringing it to a rolling boil, for 30-45 minutes, or until you have a rich-tasting stock. Strain and pour back into the pot. Sprinkle the gelatin overtop (you should have about 2 cups of stock - reduce the gelatin if you have less) and let sit a few minutes to soften. Bring to a simmer, stirring to dissolve the gelatin completely. Pour into a loaf pan or other dish and refrigerate until firm.
To make the dumpling filling, combine the ground pork, cilantro, green onions, soy sauce, ginger, garlic, brown sugar and Sriracha, mixing gently with your hands to combine.
When you're ready to assemble the dumplings, put some water in a small dish and find a clean work surface, like a chopping board. Cut the gelled stock into strips, then into pieces about 1/3-inch square. (If you like, stir the pieces of gelled stock gently into the pork mixture.)
Place a few dumpling wrappers at a time on the board, and brush around the edge with water using a pastry brush or your finger. Place a small spoonful of the pork mixture in the middle of each wrapper, along with a square or two of gelled stock. Gather the dumpling up into the palm of your hand and pleat it all around the edges using your thumb, twisting it in a small topknot at the top to close. If it doesn't stick (most dumpling wrappers are coated with a layer of cornstarch), add another drop of water.
As you fill them, put them on a parchment-lined sheet and cover with a light towel. Steam over simmering water in a bamboo steamer basket (or in a rice cooker or other steamer), on a layer of parchment, cheesecloth or cabbage leaves, for 12-15 minutes, or until cooked through. For the dipping sauce, mix the ginger with about 2 parts soy sauce to 1 part vinegar, or to taste.
To eat, pick up the soup dumpling by its topknot using chopsticks, and transfer to a Chinese soup spoon. Either poke a hole in the side with your chopstick and let the soup run out into the spoon, or lift it up, bite off one side and sip out the soup, then eat the dumpling.
Makes 2-3 dozen soup dumplings.