Cook the pierogi according to the package directions.
Meanwhile, heat the oil in a medium skillet over medium-high heat. Add the onion and cook, stirring occasionally, until soft, 5 to 6 minutes.
Add the apple and cook for 1 minute.
Add the cabbage, vinegar, ½ teaspoon salt, and ¼ teaspoon pepper. Cook, stirring, until the cabbage is slightly wilted but still crunchy, 2 to 3 minutes.
Divide the cabbage mixture among plates. Serve with the pierogi and sour cream on the side.