Sprinkle cabbage leaves with coarse salt, especially along the thick ribs. Rest for 60 minutes, turning once, then rinse twice and drain well.
Simmer the Pork:
Place pork belly, water, onion, garlic, ginger, doenjang, rice wine, brown sugar, and peppercorns in a stockpot. Bring to a boil, skim, then cover partially and simmer gently for 60 to 70 minutes.
The pork is ready when a skewer enters easily but the meat still holds together. Transfer to a board and rest for 15 minutes.
Make the Radish Salad:
Toss radish with gochugaru, fish sauce, vinegar, sugar, and scallions. Rest for 15 minutes and adjust the seasoning.
Slice and Serve:
Slice the pork belly across the grain into irregular 1/4-inch pieces. Arrange with cabbage, radish salad, ssamjang, garlic, and chile so each person can build wraps.
Notes
A bare simmer keeps the pork tender while preserving clean slices.
Refrigerate pork and accompaniments separately for up to three days; rewarm pork gently in a little strained cooking liquid.