I got the shishkabob skill in prospector, also the repairman skill there too.
I think I got those two there as well. A few others too, but its been so long I can't remember any others for sure
I can't remember if you can earn the Weapon skills in Prospector. You'll just have to try it out for yourself. You can earn some skills in Prospector, but not all, and I can't remember which ones you can and which you can't.
I took out at least 50 enemies with the sniper rifle and didn't unlock the skill (though I got Shishkabob about 10 times over during that span). Doesn't look like you can unlock the weapon skills in prospector.
In Prospector (solo) I have unlocked Scavenger, Marksman, Fast Lock and Engineer. None of the weapon skills seem to be possible.
For Fast Lock (Anti-Air Medal), it was round 3 of the Severed Ties Prospector map. Your rig is attacked by about a dozen Hawks. Takes two rockets to kill one on Normal difficulty, so you'll need to keep a bunker alive to reload.
I just unlocked the spawn with a shotgun skill.
i unlocked the weapons ones in arena DM games. I would just spawn in on that weapon and keep killing until I got it! That spawn with shotgun is key for DM.