With Windows 10, is it possible to have the clock and Volume-Adjust-Icon on all monitors in a multi-monitor setup?
As of Windows 10 version 1803 this still seems not possible. The clock will now by default display on all monitors, but the notification icons (such as the volume control mentioned in the question) only show on your "Main Display".
The only options currently available are (a) switching your "Main Display", or (b) using third party software.
we could show taskbar on all monitor. So that you could see the clock and use volume on multiple monitor. I referred link: https://www.tenforums.com/tutorials/3899-hide-show-taskbar-multiple-displays-windows-10-a.html