Three days before combine 10 cups water and all remaining soup ingredients except gelatin in large pot. Bring to boil, spooning off any foam that rises to surface. Reduce heat and simmer, uncovered, until chicken pieces are very soft and beginning to fall apart, adding more water by the cupful if necessary to keep chicken submerged, about 2 hours 30 minutes.
Strain soup; discard solids. Return broth to same pot. Boil until reduced to 2 cups, about 35 minutes. Season with salt and pepper. Pour 3 tablespoons water into small bowl; sprinkle gelatin over. Let stand until gelatin softens. Add to hot broth; stir until gelatin is dissolved. Transfer to 13x9x2-inch glass dish. Cover; refrigerate aspic overnight.
Two days before, combine all filling ingredients in large bowl and mix with fork just until blended. Cut aspic into 1/3-inch cubes. Add 1/3 of the aspic cubes to pork mixture; stir gently with wooden spoon just until incorporated. Cover and refrigerate. Return aspic to refrigerator.
Mix 1 cup black vinegar, 6 tablespoons soy sauce, and 2 tablespoons fresh ginger strips in small bowl. Cover and refrigerate. Bring to room temperature before serving.
One day prior, line 2 rimmed baking sheets with parchment paper. Place 1 dumpling wrapper on work surface. Spoon 1 very generous teaspoon filling onto center of wrapper, including at least 2 aspic cubes.
Lightly brush edges of dumpling wrapper with water. Bring 1 corner of wrapper up around filling, then pleat remaining edges of wrapper at regular intervals all around filling until filling is enclosed and wrapper forms bundle-like shape with small opening at top.
Gather top edges of wrapper together and twist at top to enclose filling. Place on baking sheet. Repeat with remaining wrappers and filling. Refrigerate, covered, for 1 day, or freeze in single layer in covered containers for 2 weeks.
On the day of, line each layer of bamboo steamer basket with cabbage leaves; place over wok filled with enough water to reach just below bottom of bamboo steamer basket. (Or line metal steamer rack with cabbage leaves and set over water in large pot.) Place dumplings atop cabbage, spacing apart.
Bring water to boil. Cover; steam until cooked through, adding more water to wok if evaporating too quickly, about 12 minutes for fresh dumplings and 15 minutes for frozen. Serve dumplings immediately, passing sauce alongside for dipping.