: If you purchased SketchUp directly from Trimble (the company behind SketchUp), your license details can usually be found in your Trimble account.
: For active subscriptions, managing your subscription details, including upgrading, downgrading, or finding your license key, can typically be done through your account settings on the SketchUp website. sketchup subd license key top
After purchase, you will receive an email with your license key and a link to download the .rbz file. : If you purchased SketchUp directly from Trimble
If you are searching for the "top" tier of SketchUp, you should know that (the $699/year plan) now includes SubD natively. managing your subscription details