Build it in the End only, over the void, at least about 130 blocks from any island, so endermen spawn only on the platform.
There are no mobs in the schematic. Put a minecart on the powered rail on top of the pillar and get an endermite into it (spawn egg or ender pearl), then name-tag it or it will despawn. The trapdoors around the pillar must be open.
Stand in the pit in the middle of the shaft floor, on the trapdoor, and hit the endermen at their feet: they land with 1 heart. The way in is from below, through the tunnel and the ladder. XP only drops from mobs a player kills.
Turn on “Hints” in the 3D view: it marks where to stand, the way in and where the endermite goes.
More about the farm and its numbers — in the article on the BeezzLand blog.
