On this page of the Wolfenstein: Youngblood trophy guide you will find a description of the achievement Right Tool for the Job. This is a bronze trophy awarded for killing a total of 75 enemies with the weapon that is most effective against their shield type.
This achievement applies only to those enemies who use armour and shields, i.e. those who have white markers above their heads in addition to the red health belt.
It is very important to read what type of shield a given opponent has. In the example from the attached picture above the opponent's head called Kugelsoldat there are horizontal rectangles.
When you call up the weapons selection menu, search for those that have the same marks next to the information about ammo. In the example from the above picture one of the "matching" weapons is Sturmgewehr.
After encountering armored enemies, it is best to look at the small graphics above their heads, withdraw to a safe place for a while and remember the weapons that can weaken their armored armor. Try to use only the proper weapons after you've started fighting.
An alternative way to read information about the use of a weapon is to open bookmarks about it in the menu (Weapons). Information about the effectiveness of the destruction of certain protective displayed in the upper right corner of the screen - it was on the training map of the gun shown in the figure.