I've spent a good amount of time finding and playing Sub Zero players.
I've also tried every setup in training mode, trying to figure out what to do against him.
He has an absolute brickwall (ice clone) that no zoning goes through, that gives him a free combo the moment you touch it. This means that Sub Zero cannot be rushed down, he'll win that game.
He has an absolute projectile with it (ice ball), that wins every tade and gains him a combo every time he wins that trade.
Coupled up with Ice Clone, this means that Sub Zero cannot be zoned. He'll win the zoning game unless you can teleport. Even then, there are no safe teleports and he can just move past his clone on reaction. So he wins that game.
Cannot be zoned. Cannot be rushed down. Overhead, low, both leading to pretty decent damage.
I find him really hard to beat. In MK9 you could hit him with projectiles through the clone at least.
So, the question stands.
How do I beat Sub Zero?
Cybernetic Kano EX knives will go through the clone, shatter it, and then hit him. Never trade with ice ball, that's always a bad idea. You can neutral duck the regular version, but not the EX. If you see him EX the Iceball, block that. EX Iceball will beat just about every projectile, and to my knowledge you cannot low profile it. I don't know what character you are using at the moment, but you just really need to go into training mode, and practice blocking his overhead, overhead string (I think it's 2,2, or back 2, 2. When he puts you in the corner he will either go for that overhead I told you, or he will go for back 3, 3, and cancel that into clone. It is up to you to not get flustered and try to mash on reaction. Learn what the fast starters you have are, and punish him for hitting you on block if he is negative. I think Slide is 9 frames, so you have to be careful, and try to think like you are the Sub-Zero player.
A problem I have, that a lot of other players have, is that we are more focused on what our character is doing/trying to do than our opponent, and they end up hitting us with things we could have punished or blocked. He isn't really that big of a threat till he gets you in the corner. Just make sure you aren't getting afraid of him and backing yourself into the corner, or you are making his job 500 times easier. Hopefully this advice helped, or will help you in the future, and good luck with your Sub-Zero slaying.