Power - You will first need to turn on power and pack-a-punch.
Parts - When you have pack-a-punch the portal will spawn at either the Nacht Der Untoten Roof, the Particle Accelerator, or the Pond. If it spawns at Nacht you can find the part next to the stairs that has the option to make the game harder. If it spawns at the Particle Accelerator you can find the part at the teleporter in between the two entrances. If it spawns at the Pond you can find the part on top of the plane part that isn't the wing. Once you get one try to find the others while you are still in there. Once you have gotten all three parts you need to down to the back side of pack-a-punch and below it there will be a bench that you can build the aetherscope at.