The Rave is a mission objective in Neon Nights in Deus Ex: Mankind Divided.
Leave the apartment for several minutes. You will need to return to it and head back inside. You will find it is much cleaner than it was before. Go upstairs and look on the bed.
Interact with the Swan Towel. This will have the information you need about the rave that Adam has read about. In it you will find the Neon Keycard. Grab it and add it into your inventory.
With that in hand, leave the building and start traveling to the South toward the Palisade Bank. It is nearby here you will find the Rave's entrance. You will see a shop with a Ludvik's sign above it. Go around the fence there and to the door behind.
Interact with the door's keycard reader to the left of it. This will open it up and let Adam inside to the Rave itself.
In the party portion of the rave, there is not too much to worry about. Head down the eastern hallway to the end.
You will find a locked room with 2 people talking in front of it. Wait for one of them to leave and then hack your way in. It only has a security rating of 1 so it can be fairly easy hack.
Inside the locked room you will find another dead person. Loot their body to find another Pocket Secretary to read with more information. This tells you that Neon will kill anyone who has neuropozyne in their system.