In a large bowl, whisk milk and pudding mix for 2 minutes. Let stand for 2 minutes or until soft-set. Fold in whipped topping. Arrange 16 wafers over the bottom of an 8-in. square dish; cover with 1/3 of pudding mixture. Repeat layers twice. Top with remaining wafers. Cover and refrigerate for 4 hours.
Just before serving, place chocolate in a microwave-safe bowl. Melt chocolate and stir until smooth; drizzle over wafers. Store in the refrigerator.