Ubuntu 18.04 Top Panel only on one monitor

Check out the Gnome Shell Extension Multi Monitors Add-On.

Just to mention it: A previous version of this post referenced to the Multiple Monitor Panels Extension, which isn't working properly in 18.04.

In Ubuntu 18.04 there is an inbuilt setting for replicating Doc (EDIT: this answer dosen't answer the asked questions but would like to help people in replicating doc for multiple monitors so just kept it here):