london
https://www.chess.com/openings you can find all opening and its variantions here
So, which one should I learn ?
You should not learn any of those. You already have some openings you are familiar with.
There are much more important and much more fruitful things to do with your time spent on chess. Tactics and endgames.
Of course, if you really want to spend your time to learn a new opening, sure, go ahead and learn whichever you want. But it won't help you get better at chess.
Hi ! I'm a beginner at chess. I know Queen Gambit, Italian Game and London system but I want to learn another opening. Which one should I learn ?