In a large bowl, beat the cream, cocoa, sugar and vanilla until soft peaks form. Arrange eight wafers on the bottom of a foil-lined 9-in. square baking pan. Spoon or pipe about 2 tablespoons cream mixture onto each. Repeat layers twice, making eight stacks. Refrigerate, covered, overnight., To serve, transfer to dessert plates. Drizzle with chocolate syrup; top with sprinkles.