In a small bowl, combine teriyaki sauce, vinegar, oil, fish sauce, sriracha, 1 tablespoon of the brown sugar and the grated ginger. Combine in a resealable plastic bag with chicken pieces and shrimp. Marinate in the refrigerator at least 30 minutes to 1 hour.
Heat grill to medium-high heat. Thread a piece of chicken, a shrimp and a pineapple chunk onto a skewer. Repeat, reserving marinade.
Transfer reserved marinade to a small saucepan. Add remaining 2 tablespoons brown sugar and the cornstarch. Bring to a boil. Reduce heat and cook 5 minutes.
Lightly oil grill grate. Grill skewers for 3 to 4 minutes. Flip over and grill 3 to 4 minutes more or until chicken and shrimp are cooked. Place on a platter and drizzle with some of the cooked marinade. Serve extra alongside.