I'm on prednisone, which takes forever to get off but I want to get a tattoo, is there a risk?

Prednisone and tatto. If Prednisone has only been for a few weeks then there is no problem. If longer, you might have a higher risk of infection due to the immunosupression caused by prednisone. Long term use also causes skin fragility. I would wait until off of the prednisone.
Yes. While there is always risk of infection, allergic reaction, and granuloma formation/scarring with tattoos, patients on Prednisone have poor wound healing and a suppressed immune system, making those risks greater.