I know most people would be well into the new Thunder Isle quest hub, but I figured this might be useful anyway. Better late than never! :)
Know Your Role can be a difficult Achievement, particularly Cheng Bo.
Most people would suggest taking the easy way out and getting someone else to do the killing for you, but hey, we're hunters! Why not solo it instead?
The easiest way I've found to do this is to stand on the hill that overlooks Cheng Bo's hut:
From here, you can clear out the mobs around the hut from a distance without having to worry about anyone sneaking up on you. Always send your pet in first before you start DPSing except when there is an Earthtalker present.
For the Gai-Cho Earthtalkers, I would recommend hitting them with a silence or stun straight off so they dont cast Earthquake. By the time they're able to cast again, they will more than likely cast Healing Wave instead, which you can interrupt again and then finish them off.
You always need to target Earthtalkers first in the pair, because they will almost always cast Earthquake under your feet, even if your pet has the aggro.
For Cheng Bo himself, he comes with two adds, one of which is always an Earthtalker.
I would recommend first parking your pet right in front of the hut, use Misdirection, then send it in to aggro the Earthtalker and quickly pull it back out. The mobs will follow your pet out, where you can stun and silence the Earthtalker from the safety of your hill.
If you want to take a helper, take Protector Yi - he's melee and he taunts, which means he will be well out of your way if the mobs target him.
Remember that you need to not have taken damage on any of the prior quests as well and you're golden! :)