To display seconds in the Windows 11 taskbar clock, follow these steps:
Open the Settings app by pressing Windows + I keys.
Click on Personalisation.
Click on Taskbar on the right side of the window.
Scroll down and click on Taskbar behaviors.
Under Clock, check the box next to Show seconds in the taskbar clock.
You should now see the seconds displayed in the taskbar clock.
Here are some additional things to note:
This setting is only available in Windows 11 version 22H2 or later.
If you have a battery-powered device, enabling this setting may consume more power.