Tie green onions and cilantro together with kitchen string. Trim and discard fat from pork, and cut pork into 1/4-inch pieces. Season with salt and pepper.
Cook pork, in 3 batches, in a large Dutch oven over medium-high heat 5 to 7 minutes or until browned. Bring pork, garlic, and 6 cups water to a boil; skim fat, and discard. Cover, reduce heat to low, and simmer 30 minutes or until meat is tender. Stir in onion-and-cilantro bundle, enchilada sauce, and potatoes. Bring to a boil over medium-high heat; reduce heat to low, and simmer 20 minutes or just until potatoes are tender.
Meanwhile, heat tortillas, 1 at a time, in a hot nonstick skillet over medium-high heat 20 to 30 seconds on each side. Wrap tortillas in a towel to keep warm.
Remove and discard onion-and-cilantro bundle. Increase heat to medium. Stir in corn, and cook, uncovered, stirring occasionally, 8 to 10 minutes or until thoroughly heated. Season with salt to taste.
Serve soup with desired toppings and warm tortillas.
Note: Store any leftovers in an airtight container in the refrigerator up to 2 days. When reheating, add water or canned broth to reach desired consistency.