Railroad team member Drummer Boy will approach you (after you've taken on a number of Railroad quests) to ask you a favor, and that'll be to destroy a group of Synths in a randomly selected area.
To get the information on the specific location, you'll have to pick up a dead drop, also located in a randomly selected part of the map.
In our quest, we were led to University Point, facing off against Synths both in the university quad and in one of the halls. After killing all the local Synths, report to Desdemona. You can play this quest a total of six times.
Note, if you have already reached The Institution by this point and haven't alienated yourself from them, the Synths in this quest will not initially see you as a threat. This gives you an opportunity to get an upper hand by laying mines and firing away at them in advance.