yourfavorite You've got a couple of options. You could browse through the Sketch Headers (e.g. @ https://github.com/abynim/Sketch-Headers/). These are the Objective-C headers for all the classes available to you at runtime. They don't include documentation, but Bohemian Coding seem to use reasonable naming conventions for the most part so it's not too tough to guess what the intent is most of the time.
Alternatively you can dynamically inspect the available methods for a particular class using Mocha's
var doc = MSDocument.new()
var docClass = doc.class()
var description = MOClassDescription.descriptionForClass(docClass)
log('*** class methods ***')
log('*** instance methods ***')
There's also a
.instanceMethods() if you want to omit any inherited methods.