Beat yogurt, milk and pudding mix in bowl until thick. Reserve 1 cup whipped topping. Fold remaining whipped topping into pudding mixture. Cut cake into ½-inch think slices. Spread half of pudding mixture in bottom of glass bowl. Top with half of cake slices; arrange half of watermelon cubes over cakes. Repeat layers of pudding mixture, cake, and watermelon. Top with reserved whipped topping. Refrigerate, covered at least 2 hours before serving.
Holiday variation: Substitute pistachio instant pudding instant pudding mix for the French vanilla instant pudding mix. Garnish with sliced kiwifruit and starfruit.
Makes 10 servings.