I have heard the following sentence in the TV series "How to Sell Drugs Online (Fast)" (season 1, episode 1, -08:22):
Niemand weiß, was unter Wasser so vor sich geht.
My first attempt of translation doesn't make any sense: Nobody knows what goes itself before like this under water.
What does "so" mean here?
Is "vor sich geht" the verb "vorgehen" = to go on, to happen? I have never seen the separable prefix in this position. Moreover, shouldn't the prefix come together with the verb in a subordinate clause like this one?