Is it safe to get a tattoo considering that i had leukemia 20 years ago that has since been in remission?

Maybe not: There has been some concern of transmission of hepatitis b and c virus through tattoong. We cannot assume that all needles and paint in tattooing parlors are sterilized appropriately. Besides, tattooing produces micro wounds to the skin with the theoretical possibility of producing wounds and infection. I would probably advice against it.

Yes, assuming....: As long as you go to a reputable tattoo artist, assuming you haven't had any long term issues from your therapy 20 years ago, you would really be at no increased risk compared to the general population getting a tattoo.