After liberating an Outpost, these will become available to you the a news board in the same Outpost. The WANTED Dead quests are shown to you via a Blue Skull icon. These are small side quests that task you with killing a enemy AI but with your knife.
Accept the mission, and you'll then be directed to a set location where the enemy is. Remember to scan the areas first tagging each person so you can find the target (shown by the Gold Star icon). Remember that he must be taken down by your knife but there are a few other ways.
Later on you can buy a Skill where you can take down an enemy and then if you're aiming at another NPC, you press to throw their knife, thus getting another instant kill. Doing this on the target also counts. The other is if your friendly NPC's (Rakyat) join in the fight. If they somehow get into a fire-fight and kill him by gun, this counts as a completing the quest.