I can not find the nightkin sniper on black mountain. I am at the radio station/jail but i can not find him.

Depends, there are several ways up and different ways to do it.

The easiest is to go up from the Hidden Valley and sneak in the back gates. You'll still need good weapons and plenty of Stimpaks because they're tough adversaries. It helps if you have stealthboys.

You can go up the road which is very tough, you'll need companions, really good weapons and plenty of ammo, Stimpaks etc.

You can sneak up the hill on the road side of the mountain but you'll probably get spotted at some point and you still have a fight at the top.

having ede helps coz he makes you able to see the nightkin on the compass even though there invisible.i dont even attempt it without the most powerful weapons coz those nightkin kick the crap outta me.the sniper has a unique missile launcher called annebelle just in case you didnt already know.dont know if its any good coz i dont use those kinda weapons.