You will need to progress the story until you unlock the Blaster Stance to get this. Once you unlock blaster stance at any meditation point unlock the Point Blank ability in the blaster tree.
To use this ability you need to be in blaster stance and press when you are near an enemy, or as an enemy is about to attack you to blast them away.
What's tricky about this achievement is you need to defeat the enemy with the ability and it is not strong enough to kill most enemies unless they are low HP. So what I did for most of my 10 kills is basically run up to the easier enemies in the game and get close to them and press .
My video guide shows the move you are looking for that will count towards the 10 kills.
