Spicy Korean chicken skewers (dak-kkochi: 닭꼬치)

Name: Spicy Korean chicken skewers (dak-kkochi: 닭꼬치)
Cuisine: Asian, Korean
Ingredients: 2 pounds chicken thighs, cut into 1½-inch to 2-inch pieces; 1 tablespoon soy sauce; ¼ teaspoon ground black pepper; 4 garlic cloves, minced; 1 green onion, minced; 1 to 2 daepa, cut into 2 inch long pieces, optional; 6-inch long garaetteok (cylinder-shaped rice cake), store bought or make your own, cut into 4 equal sized pieces, optional; For spicy red sauce; ⅓ cup gochujang (Korean hot pepper paste); ⅓ cup rice syrup (or corn syrup); 2 tablespoons gochu-garu (Korean hot pepper flakes); 2 tablespoons apple vinegar (or white vinegar); 2 tablespoons vegetable oil (corn oil, grape seeds oil); ¼ cup water; 5 to 6 10-inch wooden skewers, soaked in cold water for 30 minutes