Combine stock and cranberry sauce in a small saucepan and bring to the boil, stirring, whisking until cranberry sauce dissolves. Reduce heat and simmer for 8 minutes or until reduced by half.
Preheat oven to 170°C/150°C fan forced. Using a small sharp knife, cut around the ham shank in a zigzag pattern, about 8cm from end. Run knife under rind around edge of ham. Lift rind, running your fingers between rind and fat. Discard rind. Use a small sharp knife to score fat in a 5mm-deep diamond pattern. Stud the centres of diamonds with cloves.
Pour enough water in a large roasting pan to come 2cm up the side (this will prevent the glaze burning as it drips). Place a wire rack in the pan and place ham on rack.
Cover shank with foil. Brush cranberry mixture over ham. Bake for 1 hour 15 mins, basting every 20 minutes with remaining cranberry mixture, or until golden and glazed.