In this room, all except Joseph, wear a ties / ties.
1. Are there any punctuation errors?
2. Should it be 'a tie' or 'ties'? I think either works.
However, this sentence only means that they have the habit and custom of wearing ties. If you mean to signify a current state, such as who is wearing a tie today, right now, then use the present continuous:
In this room, all the men (except Joseph) are wearing ties.