Place half each of the onions, apples and garlic in Dutch oven. Cover with half of the sauerkraut; add bacon. Sprinkle with pepper, juniper berries and caraway seeds. Add remaining onions, apples and garlic; cover with remaining sauerkraut. Pour in wine. Cover and cook in 300°F oven for 2 1/2 hours.
In large skillet, heat oil over medium-high heat; brown pork loin. Nestle into sauerkraut; cook, covered, for 1 hour.
In same skillet, brown bratwurst; add to sauerkraut mixture along with knackwurst. Cook, covered, until sausages are cooked through and tender, about 1 hour. Transfer pork loin and bacon to cutting board; cut into slices.
Heap sauerkraut onto large platter; surround with sausages, sliced pork and bacon, and potatoes.