what will the compression test tell me related to getting a zex kit for my car?

 

condition of piston rings, if you have any bent valves.

 

so this will let me no if i can put in a zex nos kit?

 

It will let you know if you have any serious problems that nitrous would make catrostrophic. Its not going to make anything any safer if your car is in good condition, if you want to be safer get a window switch, FPR, and zex plugs.