Do students remember everything they learned in college after graduation?

Oof course no.but most important knowleges

It’s not possible to remember all the things but the specific and effective things which are common in use in the general knowledge can be remember. 

The students are not expected to remember every thing they learned in college after graduation. They are expected to use their knowledge/skills at hour of need. They should be able to find the knowledge whenever needed to refresh their memory in order to use it.

No, eventhough, their memories develop and it's potentiel increases

It depends on students - but mostly, they do if they really studied well and hard