Step 3: Test and extend the Demo Book
You can now test your datapack in game. An item named book.modonomicon.demo.name should be available in the Modonomicon creative tab and JEI/REI/EMI.
When you first open the book, it will not have proper texts instead it will have contents like book.modonomicon.demo.features.spotlight.description.
Both the weird book name and weird content texts happen because the demo book uses the minecraft translation system. You can either create a resource pack with a language file (you can copy individual lines or the entire file from https://github.com/klikli-dev/modonomicon/blob/version/1.21.1/neo/src/generated/resources/assets/modonomicon/lang/en_us.json), or you can directly type your desired text in the json files.
It is recommended to use the translation system, otherwise it is impossible for others to translate your book.
You can now edit the demo book to your liking to make your own book. Reference the Basics and Advanced sections to learn about the valid JSON keys and structures.