Lock screen notifications for apps (e.g., text messages, Snapchat®, etc.) can be customized to be shown or hidden when your screen is locked.
If a Microsoft Exchange ActiveSync® account is set up on the device, notifications are off by default.
From a Home screen, navigate: Apps icon > Settings > Sound & notification.
If Settings is unavailable, tap the Dropdown menu (upper-left) then select Alphabetical. If still unavailable, refer to Manage App Icons.
From the 'Notifications' section, tap On the lock screen.