Venting Sink

We have a sink with no vent. It had one originally going all the way to the roof but someone disconnected it and filled the vent with tar.

The sink waste line does connect to the main waste line in the house, which I presume/hope!!! has its own vent.

Do we need to vent this sink, and how do we do it, who does it, and how many billions will it cost? The sink is near an outside wall.