This mission is given to you by Lester (marked with an "L" on the map) and is exclusively for Franklin. He wants you to assassinate an important figure, who happens to be staying at a nearby hotel. He doesn't care how you do it, but he wants him dead. The target will be heavily guarded, so a direct approach is not recommended.
Head to the hotel in question and when you step into the mission marker, you will have a minute and 30 seconds to get into a good position to kill the target. The best, and easiest, position is right over the railing where the marker was located. The target is wearing a pink-like shirt, so he will be easy to notice. If you have a sniper rifle (which is highly recommended), use that.
As soon as you shoot the target, get into your vehicle and leave the area. If you are caught by any of his guards, you will receive a 3-star wanted level, and you will have to lose the cops before the mission will end. If you don't get caught, the mission will be finished once you get enough distance from the scene.