I find this varies from person to person. I have nothing to back this up, but I have a hunch it is a genetic thing, like how cilantro tastes like soap to some but not to others.

I can identify the taste of Coke Zero (or anything with artificial sweeteners) vs coke 100% of the time. They barely even taste similar to me. My wife can’t taste a difference at all.

I can assure you that one sip is enough for me to reliably identify it. Both Diet and Zero leave a very distinct and unpleasant aftertaste that's just absent on the regular one.

(doesn't apply to Pepsi though - here the regular one also tastes bad now as it contains sweeteners as well, so I doubt I'd tell it apart from Pepsi Max unless trained beforehand - they're both gross, so I unfortunately had to switch to Coca-Cola for my occasional coke cravings)

No, it doesn't taste the same. It's different from Diet Coke because Diet Coke has it's own unique formulation but Coke Zero 100% has that artificial sweetener taste.