@ousj if this is an automatic transmission, then there is no regular dipstick. The filler tube uses a special plug. You will need a service dipstick and measure the transmission fluid according to temperature and measurements on the service dipstick.
Your C-Class most commonly has the 722.6 Transmission. Check something like [https://www.youtube.com/watch?v=601a03tY0Ik|this video] to see what is involved in checking the fluid.