Can I get another ear piercing while having a keloid? Or can I get a piercing on my cartilage?

If you are prone to keloids, an ear piercing may not be a good idea since a keloid may occur. Cartilage piercings have even more risks. 

It is usually not a good idea to have a piercing when there is a keloid present on the ear.  The recurrent trauma, as well as the pressure and tension from the earring could cause further keloid formation, or encourage growth of the existing keloid.  I would recommend consultation with a board-certified plastic surgeon or dermatologist for evaluation.