From here ArcGIS Pro SDK | ArcGIS Desktop
From there... Home · Esri/arcgis-pro-sdk Wiki · GitHub
scroll to the bottom
and of course, if you select under Resources.... ArcGIS Pro 2.2 API Reference Guide
you end up at the version 2.2 reference guide
Assuming this is what you mean
Suggest you give an upvote and use case to ArcGIS Pro Help should start showing version numbers (e.g. 1.0-2.1.2) . ESRI is under the impression that you upgraded to 2.2 the day it was released, and will continue to upgrade to the latest version 3-4 times per year with every SP and version change (https://community.esri.com/thread/217032-what-happened-to-the-online-21x-help?sr=inbox ).