Can dogs / cats tell whether other dogs / cats are male or female just by looking at them, the same way humans can tell others’ gender without looking at their genitals / breasts?
Dogs and cats don’t have the secondary sexual features humans do, so I doubt if they can tell just by looking. But smell gives it away.
It’s safe to say they figure it out one way or another - trial and error if nothing else.
Smell, and yes. It’s one reason their creating ritually are so very thorough by human standards. They’re learning a LOT.
Did autocorrect mangle that sentence?
Male and female wolves differ enough in size and build that they could probably be told by sight most of the time, though they lack the secondary sexual characters in humans. But dog breeds vary so much that sexes of different breeds couldn’t really be distinguished readily.
As said, dogs can easily tell male and female dogs apart by smell. They can also almost certainly distinguish male and female humans and other mammals, since the scent signatures will be similar.
“Creating ritually” was probably “mating rituals.”
I’m assuming “cleaning ritual”.
I’m guessing “greeting ritual”
Animals don’t have gender. You mean sex.
While gender is typically used these days to indicate the social/cultural aspects of sexual identity, it is not at all wrong to refer to biological sex as gender.
“Creating ritually” was probably “creatine residuals”.
It may not be wrong, but I think it is more precise and unambiguous to refer to biological sex as biological sex.
Courting rituals.
I’m sure no one misunderstood the way it was being used in the OP.
I’ve been vaguely aware that people use the terms somewhat differently in academic circles, but didn’t realize it was such an issue. Per the wikipedia article (emphasis added):
The article referenced as #2 is here. I skimmed it, but did not see where it says that. However, it does make sense not to project human social constructs onto non-human animals.
Yes. Autocorrect is evil, hence my sig.
Ding, ding. 
Right. The use of “gender” to indicate social/cultural sexual identity is a rather recent one. In purely biological contexts, no such distinction is made.
Back on topic.
Ever see a male dog or cat try to mount another male? I have and I’m sure it’s not because they swing both ways! 
My daughter had a male bulldog. He was especially beautiful. Brown bridle with white. She kept him intact with the promise of using him as a stud. Many tries, never mounted the first female bulldog. But would hump anything else. Legs, ottomans, baby strollers, trees, male dogs. We decided he was gay. He lived a long happy life as a gay bulldog.
Most likey they are doing some kind of dominance thing, as in establishing/maintaining the pecking order. But it’s quite possible they do swing both ways. Or are outright homosexual. Homosexuality/bisexuality in the animal kingdom in general is roughly as common as it is in humans. But unless they’ve lost their sense of smell, they do know what sex the other animal is.