Kaleesh & Pheromones
TL:DR: Kaleesh breathe primarily through their mouths & save their noses for Serious Sniffing™️Vibes are communicated through pheromones.
Given that many kaleesh have a variety of serious dentition up front, most resting kaleesh face has their mouth various degrees of ajar anyway. During exertion or when someplace unfamiliar kaleesh will huff, puff, & chuff a lot of air through their mouths. The roof of their mouths are a highly vascularized membrane with what could be compared to a less precise Jacobson's organ in the middle. Their tongue doesn't really help in this regard like it may have in their ancient ancestors. Its more of the the air being captured & identified molecules being ferried off for further scrutiny in their more specialized receptor organs. This is also how they cool themselves down, since they don't sweat like we do.
They do have odor glands that secrete pheromones. The main smells come from the pair of pores behind each ear, which they often sweep along their hair & scalp, as well as a pair under the arms kind of like ours. There is a third pair of pores at the small of the back along the back of the sacrum above the booty where there was once a tail. Third pair can be very pungent but clothing helps keep anything embarrassing in check. Males also have vestigial femoral pores toward the inside of their thighs that have a unique scent that you aren't going to experience unless, you know, you're rooting around down there. Ancient kaleesh ancestors did a lot of territorial scent marking but modern kaleesh use their pheromones to read the room, so to speak.
Half of the pheromone information they are putting down & picking up can be considered anxiety & what level it is at. A lot of stress: nervousness, fear, aggression. Little to no stress: relaxed, calm, welcoming. Kaleesh can read anxiety or at least get the gist of it from other reptilian lifeforms & can learn to pick up on it from others with context.
The other half of their pheromone activity is more species specific like life stage, health, friskiness of course, & sometimes even ethnicity. Kaleeshi puberty is when you just start manufacturing all sorts of new smells which wouldn't be so bad if you also simultaneously didn't start smelling everybody else's smells AND THEN couldn't control the smells you make in response to other smells. Like goddamn.
Humans & other less scent driven lifeforms often find the smell of kaleesh to be cloying. It isn't outright foul but it isn't exactly roses & daisies. Its a bit thick, but not as sharp as the smell of rodians. It doesn't take long to get used to should one find themselves in prolonged company.
Given the sensitivity of their olfactory set up, they are rather resilient in the smells department. Kaleesh that are out & about in the galaxy don't utilize their nose unless they want to, often having their nostrils outright shut until they acclimate to a place. Kaleesh will get grumpy if there are too many loud smells. If food is too strongly flavored they will not like it & tell you it is too loud. Spicy food really hurts. They do like minty things, since it doesn't hurt in quite the catastrophic way snorting a pepper would. They are not fans of overly sweet smells & wearing a lot of perfume will keep them away from you.
Because I am an angst monger I headcanon cyborg Grievous to be completely stripped of his sense of smell & have it replaced by a hopelessly outclassed digital analog, just like his sense of touch. Like he's got sensory arrays monitoring things like air quality fed to him in a HUD & the Techno Union was like "good enough for government work." So, General Grievous is cut off from his kaleeshi-ness in yet another, incredibly debasing way. If you wanted your cyborg to keep his sense of smell you could probably swing it by packing a bunch of his nasal cavity up in the headcase.
I'll make a cute list of reasons kaleesh might be sniffing around to repent