As dogs are trained these days, it's unusual for them to attack humans. But as for untrained dogs, they may have a lot of reasons to hurt people such as people scare them and have them cornered, people challenge their whole pack, things like that (even though things like this rarely happen, the point is dogs have reasons to hurt people). So I'm thinking if a normal dog who is not afraid of humans (and is untrained) sniffs a human that smells like a cat, will the dog attack or bite?
In short: no. The whole cats vs. dogs thing is full of tropes and assumptions. This has nothing to do with smells though.
- The behavior of cats contradicts what normal socialized dogs expect. For example, a cat will move its tail when annoyed and about to attack. Dogs on the other hand will do so when being friendly/excited. Similar for growling/purring.
- Cats are usually smaller, so once they move quickly, they might trigger a dog's hunting instincts as potential prey.
- Cats and dogs can live side by side, especially when they grow up together.
- Dogs might react to smells but it's more likely one would try to find the actual origins if something doesn't feel right to them, e.g. human smelling like cat.
- Overall it still boils down to the dog's training, there's no "inherent" reaction other than sniffing I could think of.
Just as an example, our Huskies will treat any other animal they see just like a dog, unless they see it running. It doesn't matter whether it's a cat or horse.