Ubuntu 20.04 show date/time/volume on every screen

For a solution based on an official package: make sure that you have "Universe" enabled in your repositories:

sudo add-apt-repository universe

and that you're using the GNOME desktop or a derivative.

Search Synaptic (or via apt) for the package:

gnome-shell-extension-multi-monitors

Install it, along with the GNOME tweak tool (package "gnome-tweaks", not "gnome-tweak-tool" - the latter is to access some additional settings):

sudo apt-get install gnome-shell-extension-multi-monitors gnome-tweaks

You’ll have to log out and back in (sometimes just reboot your system). After that, search for the Tweak Tool in GNOME menu and launch it. Select "Extensions" on the left-hand side, and scroll till you see multi-monitors-add-on. Activate the slider.

You should see a dual monitor symbol on your taskbar. Click it and select "Preferences". This prefs page will let you tweak all sorts of options... including "Show panel on additional monitors", which is the setting that you are looking for.

Multi Monitors Add-On can do the trick.

As per Installation from git:

git clone git://github.com/spin83/multi-monitors-add-on.git
cd multi-monitors-add-on
cp -r multi-monitors-add-on@spin83 ~/.local/share/gnome-shell/extensions/

Restart the shell and then enable the extension.