I apologize it looks like Command J was a keyboard shortcut I created on my own. You can follow the article to create your own shortcut if you want. It's really easy to do and you can reduce the amount of keystrokes from the Shift-Command-D. I use keyboard shortcuts for all kinds of stuff, especially helpful for Safari for bookmarked I frequently visit.
It is Command Shift D. If you look at the arrow up, it is a shift key, not the actual arrow up. Hits like this are on macs website for keyboard shortcuts at the very top. Mac keyboard shortcuts - Apple Support