Do you have a book about India?
Do you have a book on India?
Is the first sentence is about India in general with no specific topics covered like religion, culture, education, health, politics, etc.?
And the second sentence covered all or most of the topics mentioned above?
“About” and “on” are interchangeable in such cases.
“On” tends to be used in technical or academic context.
You might want to write a book about/on India’s religion, culture, education, health, and politics anecdotally.