Preheat oven to 400°. Line a rimmed baking sheet with parchment paper.
Bring 6 cups water to a boil. Add tomatillos and boil until skins soften, about 6 minutes. Using a slotted spoon, transfer to a blender. Add onion, jalapeño, cilantro sprigs, sour cream, 1 tbsp. lime juice, and 1/2 tsp. salt. Process until smooth.
Transfer sauce to a wide, shallow bowl. Dip 4 tortillas, one at a time, in sauce to coat, and place in a single layer on prepared baking sheet. Top each tortilla with about 8 shrimp and sprinkle with about 3 tbsp. cheese. Repeat layers once. Top each stack with remaining tortillas and cheese. Bake until cheese melts and shrimp turn pink, about 10 minutes.
Meanwhile, toss together cabbage, cilantro leaves, oil, and remaining 1 tsp. lime juice and 1/4 tsp. salt, then spoon onto enchiladas. Serve with lime wedges and remaining tomatillo salsa.