1 (2-pound) napa cabbage
1/2 cup kosher salt
About 12 cups cold water, plus more as needed
8 ounces daikon radish, peeled and cut into 2-inch matchsticks
4 medium scallions, ends trimmed, cut into 1-inch pieces (use all parts)
1/3 cup Korean crushed red pepper
1/4 cup fish sauce
1/4 cup peeled and minced fresh ginger (from about a 2-ounce piece)
1 tablespoon minced garlic cloves (from 6 to 8 medium cloves)
2 teaspoons Korean salted shrimp, minced
1 1/2 teaspoons granulated sugar