Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch baking pan.
Stir chocolate cake mix, water, vegetable oil, and eggs in a mixing bowl until moistened. Beat with an electric mixer on medium speed for 2 minutes.
Spread rhubarb over the bottom of the prepared baking dish and sprinkle cherry gelatin mix and sugar evenly over the rhubarb. Pour cake batter over the rhubarb layer.
Bake in the preheated oven until a toothpick inserted into the middle of the cake layer comes out clean, about 1 hour; check for doneness after 45 minutes. Let cool before serving.
THIS CAKE IS BETTER WITH A WHITE CAKE MIX AND YOU CAN CHANGE AROUND THE JELLO FLAVOR OF YOUR CHOICE I DID THE CHOCLATE CAKE FIRST THEN DID THE WHITE CAKE I LIKE THE LOOKS OF THE WHITE CAKE MIX ...