In a large bowl, whisk together the gochujang, brown sugar, sesame oil, rice vinegar, garlic, ginger paste, smoked paprika, gochugaru, soy sauce, and salt until smooth and well combined.
Add the chicken thigh pieces and mix well until fully coated in the marinade. If you have time, let it sit for 1 hour in the fridge—but you can also cook it right away.
Thread the chicken onto skewers, packing the pieces snugly but not too tightly.
Preheat the air fryer to 400°F. Lightly grease the basket or tray, then arrange the skewers in a single layer, working in batches if needed.
Air fry for 12 to 15 minutes, flipping halfway through, until the chicken is cooked through and caramelized on the edges.
Serve warm with steamed rice, a sprinkle of sesame seeds, and sliced green onions if desired.