I’m not sure if I understand your question.
Cpanel is web hosting administration tool. cpanel also has an integrated FTP file manager. This file manager allows you to edit files on your website. You can use this file manager to access your complete website. It also allows you to edit the entire subfolder of your staging website. Beside of that you can use any other FTP client to access your production and your live website.
If you mean you use a file manager plug-in then you need to install that file manager plugin on your production website. It will show you the sub folder of your staging website and allows you to edit any files in it.
Note: Installing a file manager plug-in on your staging website will not show you the main parent folder of the staging site. It will only show you the underlying folder structure of your staging websit, one level down.