Bake the chocolate cake according to package directions in a 9x13-inch pan. Let cool completely to room temperature, then transfer to the refrigerator for 30 minutes to firm up.
Crumble the cooled cake into a large bowl, breaking up any large chunks with your hands until the texture resembles coarse crumbs with no lumps.
Add the chocolate frosting and mix with a wooden spoon or your hands until fully combined into a thick dough that holds together when squeezed.
Roll the mixture into 24 evenly sized balls, about 1.5 tablespoons each. Place them on a parchment-lined baking sheet and refrigerate for at least 2 hours or freeze for 30 minutes.
Melt the chocolate wafers in a microwave-safe bowl in 30-second intervals, stirring between each, until smooth and completely melted. Add vegetable oil if the chocolate seems too thick.
Dip the tip of a lollipop stick into the melted chocolate, then insert it halfway into a chilled cake ball. Repeat with remaining balls and return to the refrigerator for 10 minutes.
Working with one pop at a time, dip the entire cake ball into the melted chocolate, turning to coat completely. Lift it out and gently tap the stick against the bowl rim three times to remove excess chocolate.
While the coating is still wet, add sprinkles or decorations if desired. Stand the finished pop upright in a styrofoam block or stand it in a tall glass.
Let the chocolate coating set completely at room temperature for 30 minutes, or refrigerate for 15 minutes for faster setting.
Once set, store in an airtight container with parchment paper between layers, or display immediately for serving.
