Good question! My Haynes manual has no reference to the lug nut size. The good news is, that this isn't a big problem. Take the car to your local tire shop. Those guys are amazingly talented and can probably tell you just by looking, what size it is. They might even have one laying around that will fit.
Or, go to a junk yard and ask if they have a Sunfire or a Cavalier on the lot. Yank a lug nut off their junker and try it on your car. If it fits, you're good to go. If you need it for another reason, and it fits your car, you're still good to go. Just pay the man and proceed.
One other option is to go to, or call, a GM dealership and ask the friendly folks in the parts department to look it up for you.
17 inch
I'm fairly certain it's a 30mm.
thermostat? engine size?
4x6
30mm
22 and 17
36mm
6x9
M12 1.5mm
One that fits.......
6 x 9
Should be 195/70R14.