I am glad to hear about your interest in AppBuilder and mobile app development as a whole.
As I am not aware of any AppBuilder specific books, I would suggest you to look for hybrid applications development instead. I believe such books will help you a lot, as AppBuilder steps on top of the basics of hybrid applications development. Here is a link
that might give some directions.
Going further, once you create an account in Telerik Platform, you will have access to our step-by-step tutorials. They explain the core functionality among our services and clearly show how a completely functional apps can be made in no time.
Another thing I can suggest, are the AppBuilder (formerly Icenium) blog posts on falafel.com
. There are a lot of things explained there.
Finally, if you have access to pluralsight tutorials, I will strongly recommend the ones, dedicated to AppBuilder there
I hope this helps. Please, let us know if you need additional help or answers, as we are here to provide such.