In small bowl, combine soy sauce, sherry, water, sesame oil, ginger, vinegar and garlic. Pour over chicken.
Cover and cook on low heat setting for 5 to 6 hours or on high heat setting for 2-1/2 to 3 hours.
Transfer chicken to serving platter; cover with foil to keep warm.
Stir bok choy into liquid in cooker. Cover and let stand for 5 minutes. Transfer bok choy to serving dish with chicken. Sprinkle with sesame seeds, if desired. Spoon some cooking liquid over chicken and bok choy. Discard remaining liquid.