Heat a grill or grill pan to medium. If using bamboo skewers, soak in cold water for at least 30 minutes.
Thread the pork, apples, and onion onto the skewers and season with salt and pepper. Rub with the oil. In a small bowl, mix the syrup and spices.
Grill the skewers, turning (each skewer) to evenly brown, until grill marks appear, about 8 minutes. Brush with the maple syrup mixture, grill until the meat is cooked through, about 2 minutes longer. Drizzle with more syrup, if desired.