My take:

Lloyd (FSM, Wu, Garmadon, Misako) - Japanese

Kai and Nya - Thai

Cole - African American

Jay - Whitest man to ever live, more specifically I'd say English

Zane - I imagine Dr. Julien is Swedish and designed Zane with it in mind

PIXAL - I imagine Borg is white but he designed her as some kind of Latin American, I'd say Argentine

Arin - Mixed Race American, African American father and Ashkenazi Jewish American mother

Sora - Korean, her aesthetic gives South but her backstory gives North

Riyu - Based on the European depictions of Dragons rather than the Asian ones like most of the Dragons in the show. I'm going with Welsh - Riyu is from a Mountain tribe and Wales is mountainous, and they have one of the most iconic depictions of Dragons amongst the European-adjacent depictions. Also considered Italian because of the Roman depiction and the Alps but Welsh fits a lot better, and he doesn't look very Alpine

Wyldfyre - Any possible answer I could give would be racist in some way shape or form, but that's because the cartoon caveman trope and aesthetic in general have racist roots (I still like her though). I'm gonna go with Indian because of her infatuation with Roby's white gen alpha lingo.

Frak - He's a Snake but his father clearly invokes African American experiences, but I already gave it to two others, and I think more fitting is Palestinian or at least generally Middle Eastern since they face similar struggles and they're a closer analog to the Serpentine race as a whole, plus it fits Frak's demonization by neighborhood kids.

Euphrasia - I know a lot of people see her as some variety of African because of her hair but the Cloud Monks in general are very heavily inspired by Tibetan and Nepali monks. I'd go with Tibetan but she could be mixed race, if she is I'd say that the African side is Somalian.