To use your shock wave ability you first have to buy it from the upgrade menu. Once bought, hold and then press to use it. When you use this power it will shockwave enemies into the air and they will float for a few seconds. To make this achievement easier you could just upgrade your shockwave ability to increase the floating duration. While they are floating simply shoot them with a weapon, but preferably not an explosive one. To check your progress press > Extras > Player Stats > >Achievements and then find the achievement and it will have your current progress.