I’ll need a little more context to answer this properly.

Do you mean:

• Most read Jain books / granths?
• Or most read books in the world in general?

Since I am focused only on Jainism, I can best help if you are asking about Jain scriptures or Jain-related books (like Tattvartha Sutra, Samayasāra, etc.).

Please tell me: “Most read Jain books” or “Most read books in general”.