The kett devices appear to spawn randomly at various Remnant sites. Only five devices need to be destroyed to finish the Task. Devices may respawn at already cleared sites.
After locating the five devices the Task will be complete, but a new objective simply titled "Subjugation" will be added. A navpoint will be added to the map pointing to a Remnant site underground where four more devices will need to be destroyed.
An Interface Loot Box is located here. Glyphs are in the same room.