Sweet and tart pineapple juice and spicy sriracha become an intoxicating marinade for juicy pieces of pork loin, red onion, and chunks of pineapple on these skewers that have a tropical flair.
In a small pot, reduce pineapple juice to 1/2 cup over medium-high, about 20 minutes. Let cool.
Combine pineapple juice, oil, Sriracha, and 1 teaspoon salt. Reserve and refrigerate about 1/4 cup of marinade. Transfer remaining marinade to a zip-top bag and add pork and toss to coat. Refrigerate 8 hours (or up to overnight).
Heat a grill or grill pan to medium-high. Clean and lightly oil hot grill. Thread some skewers with pork, others with onion, and others with pineapple. Season with salt and pepper. Grill pineapple skewers for 6 to 9 minutes, pork skewers for 9 to 12 minutes, and onion skewers for 12 to 15 minutes, turning all skewers frequently and brushing with reserved marinade.
Put the different kebab combos on platters for guests to choose.