Finding the members of Sauron's Army in the game world | Sauron's Army (Nemesis System) Middle-earth: SoM Guide

You can either find the Army members on your own, or obtain information from the other orcs

There are two ways, in which you can find the lower rank orcs and Captains. If you managed to interrogate an orc and learn the identity of a specific Army member, the game automatically informs you of the whereabouts of such an orc. You can, then, add a new marker to the world map and reach the location. Another way is to meet the member of the Sauron's Army during free exploration of the game world and this also goes for those of the orcs that you have not managed to "identify" yet. Regardless of the circumstances, at the moment, at which you encounter an orc of a lower rank, or a Captain, the game initiates a short cutscene that will let you know who you are dealing with.

It is much more difficult to reach the warchiefs, because you need to lure them out first

As for the Warchiefs or the Sauron's Army, the process is a bit different.. Just as I mentioned earlier, you first need to lure out the selected Warchief and you do that by completing one of the missions connected with him, which was marked in red, on the map. The objectives of these missions are randomly generated so, you may need to perform a series of assassinations, within the allotted time, or eliminate a group of regular orcs, without being detected. If you manage to complete the mission (you can repeat it as much as you want to, in the case of a failure). the Warchief appears around and only then, will you be able to plan on how to kill him.