Hi there,
Once the extension is enabled, you are correct that the functionality is initially found under: View -> cell toolbar -> create assignment
To check if the notebook extension for nbgrader is installed, `jupyter nbextension list` will list the available extensions. To see if the server extension for nbgrader is installed, `jupyter serverextension list` will show if it is installed.
If you have suggestions on improving the documentation or discoverability of information, please file an issue on the nbgrader repo.
Thanks.
Carol