Wash the meat and dab dry. Score the rind with a sharp knife in a diamond-shaped pattern and rub with salt and pepper. Place the knuckle of pork on a rack over the fat pan of the oven.
Sear in the preheated oven (electric: 225 ° C/ gas: level 4) for 30 minutes. Peel onions and cut into fine slices. After 30 minutes, put 200 grams of onion slices into the fat pan and pour on 1/4 litre of water.
Continue cooking at 200 degrees (gas: level 3) for one hour. In the meantime, heat the fat in a pot and fry the remaining onion slices until transparent. Add the sauerkraut and steam briefly. Add 1/8 litre water and apple juice.
Add laurel, juniper berries and cloves. Season with salt, pepper and sugar, bring to the boil, cover and cook over a low heat for 25 to 30 minutes. Bring dumplings to the boil in plenty of water. Leave to simmer in an open pot for 15 minutes at low heat.
Turn the dumplings once in a while. Wrap the knuckle in aluminium foil and keep warm. Degrease frying stock. Pour on 1/8 litre water and beer. Pour frying stock through a sieve into a pot and bring to the boil. Stir in sauce thickener, bring to the boil again.
Season to taste with salt and pepper. Season to taste sauerkraut. Remove dumplings from the cooking bags. Arrange knuckle of pork with the sauce, sauerkraut and dumplings.