To bake the cake, follow the directions on the box. You can substitute any other cake mix, but be aware that the Trader Joe's brand makes an 8x8x2 cake, where as big brand cake mixes often make a 9x13x2, so you will either have extra cake batter or you will have less pudding to cake ratio.
Make homemade coconut pudding according to the post instructions. Mix half of the toasted coconut into the cooled pudding and reserve the other half.
Using the handle of a wooden spoon (or something similar), poke holes that are about an inch apart in your cooled cake. Spread cooled pudding over cake. Top with remaining toasted coconut. Refrigerate for at least an hour.