You need to eliminate at least 10 enemies within one activation of Nisha's action skill, Showdown. Showdown grants you enhanced damage, fire rate, and other boosts for a limited time, and it also provides auto-aim when you hold down
while shooting.
I accomplished this at level 7, relatively early in the game, with 4 out of 5 skill points in Ruthless, which extends the duration of Showdown with each enemy you kill. I used a blue Bandit SMG, which had a large magazine size (as do all Bandit weapons), so I didn't have to waste Showdown time reloading.
Fast travel to Serenity's Waste and head to the building where you obtain your first OZ kit (the small building with a satellite dish on the roof near the ramp leading to Concordia). As you approach the building, Kraggons start spawning in front of it and down in the lava. Jump around and gather them behind you. You can re-aggro them by shooting the ground near them if they lose interest.
Activate Showdown and prioritize killing the larger Kraggons first, as they split into smaller ones, which takes some time. If you leave them for last, you might run out of Showdown before you can eliminate the smaller ones. If your magazine is large enough, you can hold
+
and mow everything down after killing the big ones.
The spawn pattern varies each time (e.g., two big Kraggons or a Kraggon Immolator), so you may need several attempts. If you still can't complete it, try luring the Kraggon group to the next spawn location en route to Regolith Range, or return a few levels later with 5 out of 5 points in Ruthless and better weapons.