Short answer
Yes, a tiny spoonful of plain, unseasoned sour cream is okay for most dogs if given sparingly. It’s high in fat and contains lactose, so it can upset the stomach of dogs that are sensitive. Watch for loose stools or vomiting after the treat. If any digestive upset occurs, contact your regular veterinarian.
Sour cream — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Fat and lactose — likely to cause diarrhoea in cats and sensitive dogs.
The full verdict, portion guidance and serving notes are collected on the Sour cream food facts page.