Use a Search Combatants node to search for all enemy combatants in the scene (using the player actor as user and Is Enemy set to Yes). The found combatants will be stored in a found objects list in the event - i.e. after searching for the combatants, you need to check the count of found objects using a Found Objects Count node (should be equal to 0).
Either use this event when getting to the wall, or using a repeating Autostart event interaction that regularly checks for this.
There are also other ways to do this, e.g. with a variable that counts the killed enemies.