Turn over all of the Jackal's audio logs to the Journalist
When you hand over all 17 tapes, you'll unlock Pulitzer Material for 20 points
There are a total of 17 Jackal Tapes in the game: 1 that the Journalist gives to you, and 16 for you to find. There are 8 in the North and 8 in the South, with one in each square part of the map except for the center square in the North (where the city is), and the Southeastern square in the South (where the bar is).
You basically only get two chances to turn tapes into the Journalist, once before you leave the North, then once in the South. Both times he'll appear sitting at a table in the Bar with the rest of your buddies.
The Journalist seems to appear almost at random in the North, but usually does near the end of the storyline in the area, or once you've accumulated enough tapes. Just to be sure, when you get a mission to assassinate someone at Goka Falls, don't take the mission yet and finish off collecting the Northern tapes, and hopefully the Journalist will have appeared.
When you go to the South, the Journalist should automatically appear once you've got all 8 tapes in the area. If he appears before you have all of the tapes, don't approach him as he may not appear again and you'll lose out on the achievement.
What most people don't notice is that if you miss some in the North, you can go back and get them. HOWEVER, when you pick them up, they will not play their audio, nor will they be added to your list in the pause menu. Because of this, you'll have to make sure on your own that you've collected all of them in the North before handing over the last batch to the Journalist.
(credit goes to Codster2005 for this)