Can someone be punished or sent to jail just by holding bitcoin in banned country?
What will happen in case of trading bitcoin in country where bitcoin is banned?
Well, i think ban means cannot be used. for example if your country banning bitcoin, you wont be able to use bitcoin.
Either buy/sell or trade, you won't be able to do that with bitcoin. It must be a security reason, they cannot know the owner of bitcoin, because everyone can make bitcoin wallet without their identity.