A book of infinite words would say everything that could possibly be said. Every concept that could ever be conveyed would be conveyed in its pages. Every story that could ever be told would be told in its chapters. This book would be the ultimate source of knowledge, containing all the answers to all the questions that have ever been asked, and more.
If you're looking for ideas for what such a book might say, you could start by looking at the works of great thinkers and writers throughout history. Consider what the most influential books of all time have to say about the human experience. Also, think about what you would want to know if you had access to an infinite source of information. What questions would you ask? What would you want to learn more about?
There are no wrong answers here – the point is to get your creative juices flowing and to start thinking about the possibilities of an infinite book. Once you start thinking about it, you may be surprised at how much you can come up with!