Gumroad - The Pushing Points Topology Workbook by William Vaughan | 170 MB
Tutorial by William Vaughan (Gumroad)
The Pushing Points Topology Workbook is a 125-page software agnostic guide that teaches you the foundation of SubD topology.

There are over sixty exercises packed with loads of tips, tricks and techniques designed to teach you how to manage the topology of your meshes.
Throughout the book you will also find many images of wireframe rendered assets and their topology that you can study for reference.
This book doesn't show you how to build a car, character or creature. Instead, it teaches you the foundation of SubD topology, so you can construct ANY SubD asset with clean polygon flow.