GNOME Shell 3.6 allows users to be displayed notifications in the lock screen. By default, Gnome Shell 3.6 disabled feature the lock screen notifications due to privacy concerns. The lock screen plays much the same role as a screensaver – it is what is displayed when your device is idle. The difference between the lock screen and a screensaver is that the lock screen is really useful, of course, since it will display the time and updates about notifications
This is how you go about getting notifications to display/enable on your gnome shell lock screen. copy and paste following command on your terminal:
gsettings set org.gnome.desktop.screensaver show-notifications true
After enabling Gnome Shell 3.6 Notifications, you’ll get music player controls and the number of unread notifications in the GNOME Shell lock screen, like you can see in the screenshot below
To disable notifications in the lock screen is very easy to do. just execute the following command in terminal:
gsettings set org.gnome.desktop.screensaver show-notifications false
These tips also work with any Linux distro have installed GNOME Shell 3.6 or higher.