OnSite versions prior to 8.4, the current version you are using is displayed at the bottom right hand corner of the login screen. If you are currently logged into the system, Click on the Log Out button to be returned to the Login screen where you can view the version number. If you are using OnSite version 8.4 when you login the version number will be in the center of your screen below the OnSite Title. See video below
How Do I Check what Version of OnSite I am using?