Place chicken in a 6-quart slow cooker. Top with carrots, celery, parsnips, sweet potato and scallions. Cover with chicken broth and 1 cup water; season with sage, salt and pepper.
Cover slow cooker. Cook on HIGH heat for 4 hours or on LOW heat for 6 hours.
After cooking, uncover pot and remove chicken to a cutting board. If necessary, raise temperature to high. Add gnocchi, cover and cook for 10 minutes. Meanwhile, let chicken cool slightly, then shred meat from bones, discarding bones.
Once gnocchi have cooked, return chicken to pot. Stir cornstarch-water mixture, and add to pot. Cover and cook 10 to 20 minutes, until thickened slightly. Add hot sauce to taste before serving.