Install xfce4-datetime-plugin by entering the following commands in the terminal:
sudo apt update sudo apt install xfce4-datetime-plugin
Description:
date and time plugin for the Xfce4 panel
This plugin shows the date and time in the panel, and a calendar appears when you left-click on it.
Homepage: http://goodies.xfce.org/
Version: 0.7.0-1ubuntu1
Section: universe/x11