On this page of our guide to Batman: Arkham Knight you will find a description that explains how to infiltrate Scarecrow's safehouse. You investigate this location during the initial phase of the main story.
Head to the safe house marked by the game. It is best to get inside by breaking the glass roof. It will allow you to ambush the thugs. When you're inside, follow the game's suggestion and use a Smoke Pellet. Eliminate all the enemies (watch out for the thug who uses charge - you can interrupt it with a Batarang) and watch a cut-scene with Poison Ivy.