Dogs are allowed on Indian trains in First AC (1A) when you book the entire coupe or cabin under one PNR. They can also travel in the Brake Van as registered luggage. No other class permits dogs. Not Second AC, not Sleeper, not Chair Car. The Vande Bharat Express does not have First AC and does not allow dogs in the cabin.
A moving train does not wait. Your dog cannot tell you when he needs a break. And if you are not at a station when the moment arrives, there is nothing you can do.
Download the NTES app (National Train Enquiry System, the official Indian Railways app) before your journey. Search for your train. Look at the full schedule. It shows every station halt and the exact duration in minutes. Mark every halt of 5 minutes or more. These are your planned bathroom windows.
We did this for Goa Express 12780 before leaving Pune. Apple knew what station stops were for after the first one. Nobody was improvising. This made the 27-hour journey genuinely calm.