Howdy, asdFletcher! Check out the “Hack Yourself” section of the “Developing a Secure API with NestJS: Managing Roles” which shows you how to get the access token. Once you have the token, you can use https://jwt.io/ to decode it.
For background: the client demo app that we use in the NestJS tutorial is a React app, but this process of inspecting the access token is the same for any client app.