I have SharePoint 2013 production site for which I have only read access. I would like to know whether it is sharepoint online or on premise. Please let me know the procedure to identify whether the site is online or onprem.
You should check the response headers for version number. Online would always have the latest version of SharePoint and currently, would be running the 16 version.
That way, even though URL might not indicate SharePoint online, the version number would give it away.