Pickles — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Vinegar, salt and often garlic/dill seeds — plain cucumber is the better choice. A tiny piece rarely hurts.
Short answer
It's usually fine, but watch for signs of an upset stomach. Pickle juice is high in salt, vinegar, and may contain garlic, which are not ideal for dogs. Just offer fresh water, keep an eye out for vomiting or diarrhea, and contact your vet if you see those signs.