There;s roughly 8 locations the Knights spawn on
Earth:
Skywatch, either the Hive Loot Door or the Loot Cave/Adjacent area going to Jovian Complex
Mothyards, either the far bottom back cave before( where the Captain + Dreg or Shank + Dreg spawn, the patrol mission Hole in the Wall, the bottom cave area next to it or the far front area by the planes where the Warsat drops
Steppes, either where the 3 Hive Ultras spawn or the second furthest cave adjacent to the stair towards where you spawn into Patrol
Forgotten Shores, either the cave where those Dregs and 1 lonely shank patrol, empty huge cave or the Ship where their is tha Capatin a few vandals and a few dregs roaming the ship, the ritual is in the hull
The Divide, either the room far back where the 3 shanks + vandal spawn out from or the door to side where the 2 shanks spawn from, near a patrol marker
Rocketyard, right as you enter and where the Sevritor and Knight are going at it or the far back area where there are 2 knights + acolyte
Moon:
Archer's Line, either the warehouse where you trigger the first mission the dark beyond on the moon or the small complex outside that has a few shanks and vandal/dregs roaming on the top balcony part, right next to the warehouse
Anchor of Light, never seen it spawn here, didn't stay long enough to have info
Hellmouth, 1 is right by where the base behind the rock is, that area that has 2 caves where the Fallen are patroling, Warsat drops there or inside the base
So 6 out of 7 locations, Earth Skywatch will be the toughest to get shit done for bounty, Hellmouth the easiest, cause not many patrol the area there
Hell Earth, The Divide is the second best, after Walker event happens, it's barren for roughly 20 minutes