I worry that you don't really want an episode gate in your map. They are used to mimic the walls that appear in the Quake start map when you complete an episode. So they are only useful to block routes if a player visits a different map and then comes back to yours. Maybe it's best if you outline what you're planning and we can advise if you need an episodegate or an alternative class.
For activating triggers, what you want is a logic gate. For the following explanation, I will suppose that the trigger opens a door, and you only want the trigger to do that if the gold key has been collected.
Step 1: Create a small sealed box outside the rest of the map.
Step 2: Insert an
info_logic_inopen into the box. Modify the targets and targetnames so that the trigger targets the info_logic_inopen and the info_logic_inopen targets the door. At this stage, the trigger should still open the door at all times.
Step 3: Encase the info_logic_inopen. Create a func_wall inside the box so that the info_logic_inopen is completely embedded within it. After this step, you should find the trigger stops opening the door.
Step 4: Killtarget the func_door. Set the gold key entity to killtarget the func_door. This will occur when the key is collected. Now, the trigger should begin working as soon as the key is collected but not before.