When you receive the servo skull notification, the skull will be moving in the same direction as you.

So, say you're moving north west, the servo skull will also be moving north west.

What I do when I get the notification is immediately dash in the same direction as I was going, search it out among the mobs a short sprint ahead.

It's not very strong so should be easy to kill. I've never had a fail on a servo skull before, even in a room full of mobs.

Part of the challenge is finding and killing it before the 30 secs pass by so I doubt they'll add it to your minimap (same for those cogitators where you get the notification but they also don't show on the map).

It depends on your character and build too, make sure you either have a mobility skill that lets you zip around like the aether blade or make sure you have a lot of movement bonus. That really helps.

its hard to keep track or even find it when the screen is full of enemys, it looks like the little skull you can add as your pet just bigger... first few voids i missed them but mainly because i didnt focus or even knew that the skull is found on that map (its shown above the mission on void map;)

it's a good idea to add a skull icon on the minimap to it, like villains and elite