On this page of our guide to Wolfenstein: Youngblood you will find a detailed description of The Robotermorder side mission. This task concerns to track down and destroy the title soldier robot, which is a stronger variety of Robotersoldat.
Who's commissioning the mission: Talk to Anais Fontaine at the catacombs - resistance's hiding place.
This task is performed in the Riverside district, which you visit during the second main mission and during the raid associated with Laboratory X.
Once you reach Riverside, travel the streets until you reach the gate shown in the picture. The sisters will be automatically attacked by Robotermorder.
Robotermorder is an advanced version of the well-known Robotersoldats. It is much stronger and can move much faster. Use your weapons capable of destroying "horizontal" rectangles on the armor bar of Robotermorder.
A mini-boss will run around a lot when attacking sisters and may also jump on the walls of buildings. You can then continue to attack it, although the risk of missing and wasting your ammo increases.
Withdraw sisters if you take more damage and need to look for supplies (there is a residential building in the area) or activate pep signal. There shouldn't be any other enemies around, fortunately, and you can focus solely on your mission. After the destruction of Robotermorder, return to Anais in Catacombs.
Rewards: 12400 XP, 620 silver coins, 1 skill point.