How to show dock on all monitors in Catalina?
This isn’t how the dock works. Apple puts it on one screen only. 

You can do some setting with mission control and hiding, so you might be happy with that. 


How to get a dock on multiple monitors
Is it possible to have my dock visible on all monitors in El Capitan?
show dock permanently on the primary display only or simultaneously on both displays


You could use a third party app to make a launcher window on multiple screens or move to using a keyboard based launcher like LaunchBar or Alfred.