Can you use UV-C light to sanitize reusable masks?

Probably.  I leave mine on my dashboard when I drive to a different site. 

Absolutely yes you can use type c germicidal fluorescent light to sanitize the mask and kill everything that's in or on the mask. don't look at the light don't expose yourself to it this light kills everything biological that gets exposed to it including your skin or your eyeballs

@BlockingBack: Just so you know, nearly all solar-originated UVC light is blocked by the atmosphere, and your windshield is also designed block UVB, and some UVA. Your side windows block less UVA.
Anyone using a UVC lamp should carefully read the instructions and use eye and skin protection.

I wouldn't try it....   so no!
You might miss some areas, or do it wrong.  Also virus may be embedded in the cloth.

You could, but that's really overkill. You can essentially get the same effect by leaving a mask in bright sunlight for 6-10 hours. The CV-19 virus isn't going to survive on a porous surface that long anyway.

Yes, but I don't know how strong the UV must be or how long the mask needs to be exposed to it.