To make the dip: combine pesto, sour cream, and mayonnaise in a small bowl. Add salt and pepper to taste. Cover and chill until ready to serve.
To make caprese skewers: if using a large fresh mozzarella ball instead of the bocconcini, cut the mozzarella into large cubes, about 1/2 inch in size. On a small bamboo fork skewer or toothpick, add a cherry tomato, piece of fresh torn basil, a bocconcini or piece of mozzarella, another piece of fresh torn basil, and a final cherry tomato. Repeat until you have about a dozen skewers or run out of ingredients. Arrange with dip on a platter and serve.