Cut pork into 12 pieces and pound into scallopine about 1/3 inch thick. Season with 1/2 tsp. each salt and pepper
Heat 1 Tbsp. oil in a large, nonstick skillet over medium-high heat. Add half of the pork, without crowding pan, and cook, until nicely browned on bottom, about 3 minutes; turn and cook until pork is cooked through, about 3 minutes more. Transfer pork to a plate. Repeat with remaining oil and pork.
Add onion and wine to pan; cook over medium heat, stirring, until onion is dry, about 2 minutes. Add broth and apple; simmer until liquid is reduced by half, about 5 minutes. Add butter and remaining 1/4 tsp. salt; stir until incorporated. Remove pan from heat, add pork slices to sauce and turn to coat.
Arrange pork on plates, spoon sauce and apples on top and serve.