1. Make chicken: Whisk coconut milk, fish sauce, curry, sugar, cilantro, salt and pepper. Put chicken in a large ziplock bag; pour in marinade. Seal bag; rub marinade into chicken. Chill for 3 hours, turning bag occasionally.
2. Make sauce: Combine soy sauce, vinegar, red pepper, sugar, ginger, sesame oil, peanut butter and broth in a pan and bring to a boil over medium heat, whisking until smooth, 2 to 3 minutes. Thin with more chicken broth, if desired. Remove from heat, let cool, cover and chill.
3. Preheat grill to medium. Remove chicken from marinade; discard marinade. Thread each piece of chicken onto a metal or bamboo skewer. Grill for 5 to 7 minutes, turning once, until chicken is cooked through and no longer pink. Serve with sauce.