To get a pop-up notification, you can use notify-send. This gives you a notification using the same popup popup as the OS used for new mail, etc. This is not modal, so it will only last a certain amount of time. You can increase the time with the -t option.
Zenity will provide you with a modal popup that you can manually clear. Use something like:
zenity --info --text="message text"
Nerdfest
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