A referee can go anywhere on the pitch, they are constantly on the move. They just have to stand in a position where they have a clear view of the ball.
Close to the action but not so close as to get in the way.
looks for fouls and reffs
The players themselves and the referee, but accidents can happen so there is alway a team doctor, physio and paramedics on stand by.
the net the players the referee the field the ball
All over the field.
23.... 11 from each Team and the Referee.
In the end it's the referee and ONLY the referee who makes the call, but if a linesman sees something illegal on the field he can raise his flag to notify the referee that he has seen something and then tell the referee what he saw.
There is 1 referee on a soccer field. Three others are along the touch lines, two assistants and a fourth official.
Play continues. The assistant referee is considered part of the field just like the referee. You may be sure that the referee will address this inattentiveness issue with the assistant referee at the half or after the match.