You reach the Void at the end of the first chapter of Darksiders Genesis. Trickster Door is in the side part of the location. This page of our guide to Darksiders Genesis has a detailed solution on how to open the Trickster Door.
Immediately after entering the Void you have to approach the rock glowing red. Destroy the object to get a new weapon.
After that, you will get Vorpal Blade. It is a massive object that looks and works like a shuriken.
This weapon allows you to attack enemies from a distance and helps you open many secret passages.
To open the passage, you must mark two targets and throw the Vorpal Blade to activate them both. This creates a passage between the rocks.
To open the Trickster Door, you need to have two keys. You get one in the first chapter. The second can be purchased from the store.
The room is full of resources and cores. Thanks to them, you will develop your characters much faster.