Google Chrome Shortcut Key / Hotkey to duplicate a tab:

* First, press Cntrl + L to focus on the address bar.

Then
Press Alt + Shift + Enter (Does not navigate to the new tab - SAME WINDOW)
or
Press Alt + Enter (Immediately navigates to the new tab - SAME WINDOW)
or
Press Shift + Enter  (Immediately navigates to the new window/tab - NEW WINDOW)