Soak skewers in water 30 minutes. Pound garlic, chile, and sugar to a fine paste with a mortar and pestle. Stir paste together with vinegar, fish sauce, water, and lime juice. (Alternatively, puree sauce ingredients together in a blender.) Pat scallops dry. Thread 4 on each skewer (flat sides facing out; see photo), then brush both sides with oil (2 teaspoons total for 4 skewers). Season scallops with salt and pepper. Brush a 12-inch nonstick skillet with remaining teaspoon oil and heat over high heat until hot but not smoking. Sear scallops, turning over once, until just cooked through, about 6 minutes total. Serve scallops with sauce spooned over.