I have a Jupyter hub installed and I was wondering if it is possible to share notebooks among different users.
You can share a Jupyter notebook is to simply to place it on GitHub (and view it directly) or some other public link and use the Jupyter Notebook Viewer. When privacy is more of an issue then there are alternatives but it's certainly more complex, there's no built in way to do this in Jupyter alone but a couple of options are:
Host your own nbviewer GitHub and the Jupyter Notebook Veiwer both use the same tool to render .ipynb files into static HTML, this tool is nbviewer. The installation instructions are more complex than I'm willing to go into here but if your company/team has a shared server that doesn't require password access then you could host the nbviewer on that server and direct it to load from your credentialed server. This will probably require some more advanced configuration than you're going to find in the docs.
Set up a deployment script If you don't necessarily need live updating HTML then you could set up a script on your credentialed server that will simply use Jupyter's built in export options to create the static HTML files and then send those to a more publicly accessible server.