How do you find out who owns the rights to a given book?

I just read a brief summary of India's copyright law. The copyright for the work as written by Ghosh survives him for a period of 60 years, so it would be among his assets to be distributed to his heirs upon his death, no matter who he claimed owned it when he was living.

If he had a will, it might have named the person, organization, or institution to whom the copyright was to go, or it might have overlooked the copyright. If he did not have a will, there are laws about surviving blood relatives receiving the estate.

So the next step, in the absence of cooperation from the publisher, is to find either his attorney or closest living relative.

Best book awards from https://bestbookawards.org.uk/

Copyright stays with the author plus time after that,  held by the estate in this case.

Me? I don't. You do. I don't care. Still, I hope this somehow helped.

Strange.  Here is all that is on Amazon:  "Very little is known about the author of this book apart from the facts that he is a retired Government of India officer, now in his late nineties, apparently hoary, but healthy. When requested for more bio-data, he wrote back…The Real author of the Original Yoga is the Lord Siva. In the mundane world, Patanjali is the prime propagator of yoga. Any other claim to authorship, therefore, cannot but be spurious. …It is Truth that matters, not the utterer of the Truth. No Truth ever becomes a bit truer even when repeated by the most distinguished person. …Hence all genuine aspirants of yoga "