it should be at the front of the engine close to the bottom. I don't believe this is something you can check to prevent customers from using just any fluid. If I'm not mistaken, a special tool is required to remove the dipstick. I'll check on this to be certain.

 

go to www.courtesyparts.com click 350z. at top of page click 7 things you need to know about your z and it explains it