1.Combine pork, sauce, sake, sugar and grated ginger in medium bowl. Drain pork over small bowl; reserve marinade.
2.Discard thick ribs from wombok, cut leaves into 4cm (1½-inch) squares.
3.Heat oil in wok; stir-fry pork, in batches, until browned. Remove from wok.
4.Return pork to wok with cabbage, reserved marinade and juice; stir-fry until hot. Serve with steamed rice and top with chopped green onions, if you like.
To obtain ginger juice, squeeze grated fresh ginger into a sieve set over a bowl. A piece of ginger measuring about 15cm (6 inches) in length will yield 3 tablespoons of grated ginger; this amount of grated ginger should in turn yield the 3 teaspoons of juice used in this recipe.