You can use try using
"LoginWindowMessage " on com.jamf.connect.login .
A custom message to display in the lower-center of the login window.
If you are using a Jamf Configuration profile you should be able to use the standard Jamf varaibles. Try $COMPUTERNAME in the profile setting.
However, a word of caution. This is a not a dynamic variable. The variable is populated by Jamf when the profile is pushed to the computers. So, if you are pushing your Jamf Connect Login profile in a prestage or early in the deployment process and then change your computer name later, the profile will still reflect the old computer name.