The GI Pups are one of Putty's many enemies within the game and the first kind you will bump into from the first level. These guys don a green army style helmet with green overalls to match too and walk along platforms waiting for you to punch there lights out!
In Level 1:1: Tomb of King Phut, there are 15 Pups to kill. None of them are hidden or hard to find but I've put together a quick video to show where all the Pups are within the first level.