Add a second clock to the Windows taskbar

1. Right-click the clock in the taskbar
2. Click Adjust Date/Time
3. Click Add Clocks For Different Time Zones (Windows 10) or the Additional Clocks tab (Windows 7)
4. Select Show This Clock, pick a time zone, and then add a descriptive label for the custom clock
5. Click Ok

https://www.techrepublic.com/article/how-to-add-a-second-clock-to-the-windows-taskbar/