My buddy just bought a omega Z5 and now he wants know everything about is so if anyone has any information plz let me know

Have him read his manual from front to back until he understands all aspects of the rifle. Then read it again.

After that make sure the rifle is nice and clean before you go to the range. Start with 100 grains of powder and T/C projectiles and that should be a good start. .

what type of nipple should he use?

this is an Omega.. there is no nipple. The rifle uses a 209 primer, the same as would be loaded in a shotgun shell. All that is explained in the manual.