I would like the lock-screen clock and the wingpanel clock to show seconds. Is this possible?
Yes, you can use Dconf-editor or Configurator and go to
com.canonical.indicator.datetime and enable
Or just paste this in your terminal:
gsettings set com.canonical.indicator.datetime show-seconds true
If you don't want to show seconds anymore you can use this:
gsettings set com.canonical.indicator.datetime show-seconds false
When I use that command it says:
No such schema "com.canonical.indicator.datetime"
Edit: the correct setting is:
(under dconf Editor) io.elementary.desktop.wingpanel.datetime -> clock-show-seconds