Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch pan.
Mix cake batter according to package directions, adding water, oil, and eggs as directed. Spread batter into prepared pan and bake in preheated oven until a tester comes out clean, about 30 minutes. Cool and crumble. Make pudding, according to package directions, with milk.
In a large trifle or other glass serving bowl, place half of the crumbled cake. Pour half of the coffee over the cake, and spread half of the pudding over that. Top with half of the whipped topping, sprinkled with half the crumbled candy bars. Repeat layers in the same order. Refrigerate until serving.