For the Pork Kebabs:
Whisk together pineapple juice, soy sauce, lime juice, mirin, garlic, ginger, sesame oil, sriracha, cumin, and coconut palm sugar. Taste and adjust seasoning as needed. Measure out 1 cup of the marinade and set aside. Pour remaining marinade over the pork and marinate in the fridge for 3 hours or up to 24 hours. Thread skewers with 3 pieces of pork, 2-3 pieces of pineapple and 2-3 pieces of onion, alternating between the three.
Prepare a grill to medium-hot or place a grill pan over medium-high heat. Grill the skewers, flipping every 2 to 3 minutes, until lightly charred all around, 8 to 10 minutes total. Remove from the heat and transfer to a serving dish.
Garnish with cilantro and serve with dipping sauce.
For Dipping Sauce:
Pour the reserved 1 cup of marinade in a small saucepan and bring to a boil, then reduce to simmer. In a small bowl, whisk together cornstarch and water. Pour the slurry into the saucepan and cook over medium heat, whisking constantly, until thick, about 3 minutes. If mixture gets too thick, add more pineapple juice, 1 tablespoon at a time, until sauce is thick and coats the back of a spoon.