Heat a large skillet over medium-high heat. Brown pork chops in the hot skillet, 2 to 3 minutes per side. Drain grease.

Arrange apples and onion in the bottom of a slow cooker crock; top with browned pork chops. Pour in enough water to cover the bottom of the crock.

Cook on High for 3 hours or on Low for 6 hours. Stir in sauerkraut and fennel seed and continue cooking for 1 hour more.