Look for C:\Program Files\Cakewalk\SONAR Platinum\SONAR Reference Guide.pdf
 
It's from 2015, so it's not current with the rolling releases since then, but it covers a lot.  Plus it's nice to be able to scroll through the 2000+ pages and see all of the topics without having to jump from an index. 
 
Then there is always the online help for the new features ...