There are few places you can actually get this in the game. The easiest should be Level 1-2. After you drop down from the long ventilation shaft right on top of an enemy, this is where you start. Defeat that enemy with roll and head to the left. Move as fast as you can, defeating enemies as you see fit as you go. There are more than 10 here, and the first enemy you drop down on out of the vent is far from the others, so you can probably consider the next enemy you defeat the starting point. If you do not get it by the point you get to an enemy standing by some red boxes next to an elevator shaft, you went too slow. Try again.