Preheat oven to 230°C. Place pork on a rack in a large roasting pan. Pat rind dry with paper towel. Drizzle over 1 tbs oil. Sprinkle the salt over the rind and massage it into the skin, especially the scored areas. Roast in the oven for 45 mins or until the rind begins to blister. Reduce heat to 200°C and roast for a further 1 hr 15 mins or until pork is cooked to your liking. Cover loosely with foil and set aside to rest for 10 mins.
Place the sweet potato on a baking tray lined with baking paper. Drizzle with 1 tbs oil and toss to coat. Season with salt and pepper. Roast in the oven with the pork for the last 50 mins of cooking.
Meanwhile, heat the remaining oil in a large heavy-based saucepan. Add the onion and cook, stirring, for 5 mins. Add the garlic and cook for 1 min. Add cabbage, apple, sugar, cider, vinegar and butter. Season with salt and pepper. Cover and simmer over low heat for 1 hour.
To make the gravy, pour the pan juices from the pork into a saucepan. Add flour and stir over low heat for 1-2 mins. Gradually whisk in the cider and stock until smooth. Increase heat to medium and simmer for 5 mins or until thickened slightly.
Slice pork and divide among serving plates. Serve with braised red cabbage, sweet potato, steamed greens and gravy.