Can't find the activity or gang operations that will allow me to take control of territory in Loren Square, Steelport (Morning Star territory)
Solution 1:
Found a map of gang operation locations - click to enlarge:
Source: http://saintsrow.wikia.com/wiki/Gang_Operation
The lower-right uncontrolled gang operation in my question is actually located in another territory (as seen in the screenshot of the map in my question). This is probably why I haven't found it by driving around. The middle one is a bit tricky as it is actually located on top of a high-rise building, so you'll need an aircraft to spot and attack the gang in there.