checkin the transmission fluid on 1998 Cadillac Catera

i need to check my transmission fluid level does the car need to be running or turned off to check it?

Asked by for the 1998 Cadillac Catera
There is no stick. It is a sealed unit and I have been told that only a Caddy dealer can service it. I was told in the past that it cost $400 to service but later the same person said $200. My radiator went out on my move to my new location and I liked driving it so much I got a 2001 a few months a go.