first off, that completely vague and doesn't tell me what area you are in. my guess you are in Downtown. A red dot means that's where an enemy is for Chase to fight and save a civilian.
Or if you already saved the civilian it's just a glitch that happens when you complete most of the tasks on the map, this happens in other areas such as squirrels in Bluebell Woods, or the bird in Albatross Island
As for the second question. can you be specific what area you are in. The side objectives depend greatly in what order you play the game, for example i may have found everything and for me the last tourist spot would be in Downtown but for you, perhaps you found everything in Downtown and need help in Fort Meadows, so "last" varies