Prepare the cake mix according to package directions and bake in a 13 by 9-inch pan. Let it cool thoroughly, then cut the cake into cubes about the size of walnuts.
Prepare the chocolate pudding according to package directions.
In a medium bowl, whip the cream with the sugar until stiff.
To assemble: In a trifle bowl, layer half the chocolate cake cubes, pudding, whipped cream, chocolate sauce or syrup and nuts. Repeat, layering the remaining ingredients, ending with whipped cream and nuts. Drizzle decoratively with chocolate sauce or syrup.