Judith explains how the Nageeg work. This is, of course, shown more in-depth in the light novels (like everything else is when it comes to Judy), but if you need a screencap reference... Here ya go.
Updated 7/20/2024
Vesperia’s Ultimate Guide pretty much confirms that Krityans can use artes without the use of bodhi blastia. Which we kinda had an inkling about anyway, but I remember people pondering where Judith’s bodhi blastia was.
Yuri and Estelle’s are their bracelets, Flynn has it on his chest, Karol’s his bag, Raven has his knife, Patty has her binoculars, and Rita has her necklace… But nothing was said for Judith nor was anything shown in her concept art.
Well, short answer is: She doesn’t need one. Her nageeg is why she can use artes.
And while this may seem like an asspull, recall that one side event where you go to Temza and a Krityan is trying to use artes (you unlock one of Judith’s artes for this event, but I don’t remember what). He wasn’t wearing any bodhi blastia either.