+ 1 to the Sonar Power series. I have owned several versions of that, including the latest X3 version, and it is always a nice alternative to have for some how-to instructions or a refresher on a rarely used topic. It has a chapter on soft synths, and two chapters on effects. Also a chapter on basic editing, and one on advanced editing.
The Sonar user manual is mostly a reference guide, other than a few tutorials, which are highly recommended for new users.
I'm sure most of the X3 info still applies to the core Platinum and CbB, with the exception of coverage for new or updated features since 2015. The basics are still the same.
There is also a lot of info on these pages announcing the introduction of new feature in Platinum as they arrived, covering the period from 2015-2017.
https://www.cakewalk.com/.../SONAR/Whats-New#start Look especially for links to the Tech + Music publications listed in the 2017 monthly update announcements, as well as the older eZine.pdf publications prior to that. There are a wealth of articles including how-to details for popular new features.