"The bag of the man who is sitting is empty" would be a bit better. This Korean is probably wrong, too. It's most likely 앉아 있는 남자. No one has time to talk about the 앉는 남자 before he completes his sitting down.
If a suitcase, purse, briefcase, sack, or paper bag is called something other than 가방, I can't think of anyone carrying one. Can a native speaker please explain what is and is not a 가방? I tried briefcase, but was wrong.
"The bag of the sitting man is empty." shouldn't be wrong, should it ?
I put "the sitting man empties his bag" can someone explain why this would not be correct?
The bag in your sentence is an object. The bag in the Korean one is the subject.
You're attributing an action to the man. He's not doing anything, though. The sentence is just informing on the status of his bag: empty.