If you hit `C-h b` you get a list of all the current keybindings. `C-h m` lists the keybindings focused on the active modes. You can search either for the functionality or binding you're looking for. Also, `C-h k` followed by any keybinding will describe the keybinding. If you get the documentation of a function or command with `C-h f`, it'll also mention the keybindings it's bound to, if any. All these `C-h` help keybindings are described if you hit `C-h C-h`, and they're also mentioned in the tutorial that's linked to when you start up emacs for the first time on default configuration.

These helps are also available in the GUI menu bar, for example Help > Describe > List Key Bindings, which also mentions the keybinding `C-h b` to the right of that.

How is discoverability of keybindings lacking?