What is the item on the back top of the outside of a 02 Clk 320
On the back trunk over the long center brake
light
Does your rear end look like this? If you are talking about a piece that sticks up, that would be the spoiler. It helps with airflow and it looks cool. That's all lol. If it's something else put a picture up so we can see what you're asking about, then we can hellp you better :D
Radio, phone, navigational, or emergency locater service like "On Star" that GM has. If it is a black shark fin looking piece, it is an antenna.