This is easiest to unlock in the third mission called Level Zero
. This is a training mission with 4 areas, the second area has you pitted against training dummies to teach you the combo moves.
move to be trained is the Juggle
instead of following the onscreen instructions use this opportunity to hit the 6 training dummies placed in front of you with the Panda Stumble (Hold
To achieve the 5 hit combo you need to hit 5 dummies at once as there wont be enough time to maintain the combo by rebounding off the walls.
Here's a video demonstration.