I see several things going on here, but let's start with the most likely.
In your Book model, you have a naming convention wrong. Normally this just makes it harder for someone else to understand your code, but in this situation I think it's stopping JavaFX from recognizing your model properties. You have methods like this:
...that should look like this:
I think without that get in the method name, JavaFX doesn't know how to find the property method. Now uncomment 67-71 in BookScreenController.