Place the sliced sausage and chopped onion in a skillet over medium heat. Cook until the sausage browns lightly and the onion softens, then drain any excess fat.
In a mixing bowl, stir together the cream of mushroom soup, milk, paprika, salt, and black pepper until smooth.
Add half the cubed potatoes to the slow cooker. Layer half the sausage mixture on top, followed by half the shredded cheddar cheese. Repeat with the remaining potatoes, sausage mixture, and cheese.
Pour the soup mixture evenly over the layered ingredients. Cover and cook on low for 6 hours until the potatoes are tender.