What German phrase did you have in mind? Because the idiomatic translation of "to pay attention" is "aufpassen", which literally translates to something like "pass on" or "fit on".
Edit: "to pay attention" is literally "Aufmerksamkeit zollen"
Sure, just like you can't separate "pay attention". Both are idiomatic. But you can separate "aufpassen" into "Paß auf". (For the benefit of non-German lurkers, "Paß auf" is a command to pay attention.)
The literal analogue to "pass on" or "fit on" is "anpassen"; "auf" generally means "over", "on/to the top of".