Leonora Johnson is a dead San Andreas resident in GTA 5.
You need to find all 50 Letter Scraps around the map.
After gathering every Scrap, Franklin will be led to the home of Peter Dreyfuss. After confronting Dreyfus, Franklin is given the option of giving chase or letting him go. Choosing to pursue and assassinate him completes the mission A Startlet in Vinewood and the A Mystery, Solved Achievement.
Map and last paragraph of solution : Ign.com