Cooked duck — Food safety facts
Safe to share · Dogs · full breakdown on the linked food page
Plain cooked duck breast without skin is fine occasionally. It is rich, so skip the skin and fat.
Short answer
Yes, plain cooked duck breast is safe for dogs occasionally. Make sure it's unseasoned and you remove all skin and fat since duck is quite rich. A small piece now and then is fine, but go easy on the portions. Watch for any vomiting or diarrhea after eating it, and call your own vet if anything seems off.