There’s a great page in the docs (Working with messages : Node-RED) that will explain how to use the debug panel to find the right path/value for any data item.
Pay particular attention to the part about the buttons that appear under your mouse pointer when you over hover a debug message property in the sidebar.
If you select Copy Value for the payload out of the book node then you can paste it here, in a form that can be copied and pasted into an inject node for testing, and so that we can see exactly what you have.
When you paste it, in order to make code readable and usable it is necessary to surround it with three backticks (also known as a left quote or backquote ```)
```
code goes here
```
See this post for more details - How to share code or flow json
