OH that's a tough one. You need to learn the whole list of modals. But let's start here: be supposed to = sollen Sollst du nicht mitgehen? = Aren't you supposed to go along? Du sollst öfter hierher kommen. = You'r supposed to come here more often. supposedly OK = es geht angeblich it should be OK = es sollte gehen supposedly = 1. angeblich (it has been said); 2. vermeintlich (It is thought) There is a lot more detail in the dictionary.

It really depends on what you want to say exactly. There's no direct translation of "supposedly". She was supposed to go shopping (but didn't) = "Sie hätte einkaufen gehen sollen (hat es aber nicht getan)." It's supposedly ok to smoke here = Depends heavily on the situation. "Es ist wohl in Ordnung, hier zu rauchen" as a statement. If you say it as an answer to someone who's asking you to stop smoking, "Aber man darf doch hier rauchen, oder?". Etc.

You could use the conditional as well to express ' was supposed to do something' ,because she didn't do it in real. "Sie hätte -------- sollen" "She was supposed to ----."

Thank you all 3: Elliot, Cherry and Dirkt for the answers. They were all very helpful