Sometimes, for whatever reason, I need to find out the exact version of Joomla a site is running without being able to access the administration area.
Here's where to find the version number in the file system.
Open the file:
You should see the major and maintenance version near the top of the file:
/** @var string Release version. */
public $RELEASE = '3.4';
/** @var string Maintenance version. */
public $DEV_LEVEL = '8';
The above would translate to version 3.4.8
I've needed to use this in the past to fix hacked sites where it was not possible to log into the administration area and I needed to replace the core files and wanted to use the same version as the installed site to avoid any issues with the database.