The Charge Jump is the 2nd to last skill you acquire in the game. It is located in Sorrow's Pass. To do a Charge Jump, you need to hold the
for a second then tap the
button. Now to get the cheevo, you need to make sure there is an enemy directly above you when you do your charged jump. The easiest enemies to do this on are the slugs that traverse the ceiling in the tunnels.
Easy as that...