Ooh interesting. We can already rule out Nakime and Kokushibo since they already have jobs in Kimetsu Gauken as Muzan's secretary and the Kimetsu Academy's Vice Principal. But if I had to give them alternate jobs, Kokushibo would be a businessman and Nakime would be a musician.
I know cannonically Douma is a scam artist but let's be honest if he had an actual job he'd be a male model.
Akaza, Gyutaro, Kaigaku, and Ume are still students cannonically but if they had jobs then Akaza totally would be an instructor at his father-in-law's dojo, Kaigaku I feel like he'd be a mechanic of some sort, Ume would either be a successful influencer or model and Gyutaro would be her agent/editor/bodyguard for the sole purpose of keeping an eye on his precious sister.
Hantengu and Urami are old farts that just sit at home tired and retired. I can see Sekido as a bouncer or bodyguard for an establishment since his attitude seems like a good fit, possibly also a mechanic. Let's be honest Karaku is an exotic dancer. Urogi would either be an exotic dancer as well but I also like the idea of him working in a bird sanctuary. Aizetsu would probably prefer a peaceful and less stressful job, so I like the idea of him working in one of those famous dog or cat cafes or maybe a librarian. Zohakutan is a tough one. I think he'd be a mechanic too or he'd work at a comic/game shop.
Hairou is a soldier or some kind of officer. Kyogai is already a music teacher but alternatively he'd be a writer. Enmu is a doctor obviously but not a good or legit one. Gyokko I feel would be an artist. Again not a good one because of his gruesome and weird tastes so he'd have to get a second job like a regular office job or something to support himself. Muzan's a politician of course.
Rui is still little but I can see him being a scientist when he grows up studying insects and other wild life.

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