For Needle Pumper, you need to get stealth kills using the syringe. There are only two levels with a syringe in it, Rosewood and Death Factory. Rosewood, however, is easily the best.
Load up Rosewood and take the second checkpoint called the Orphanage Halls. When the checkpoint starts, wait for the guards above to turn around and follow them down the hall. Take the second right and then slip through the next room and into the hallway on the right. On the right side of this hallway will be a lab room. The island in the middle of the room should have a syringe on the closer end. Grab that and get to work.
It may take you reloading checkpoints a couple of times to get. There is a challenge on Rosewood called "Subtle Injection" that you should end up working towards at the same time. Just work towards those and you should get this style in no time.
