What are the symptoms of a blocked vent pipe from the roof? Is possible for the sewer gas to come through a trap (full of water) when the vent pipe is blocked?
Thank you in advance for any help!

Blocked vent usually cause gurgling in the drain. Speedball1, the plumber, recently explained to me that bubbles in the toilet indicate a blocked drain and not a vent. I learned from his explanation. A blocked vent could cause a P trap to be siphoned out. Sounds like you have an odor and are looking for the source. Sewer gas and rotting hair both stink, are you sure which one you have? Most common source of sewer gas is a failed wax ring under the toilet.

When your fixtures begain to talk back to you they do it in two ways. They "gurgle" atcha or they "bubble" atcha. The "gurgle" is caused by vacuum caused by a blocked vent and the fixture vents through a fixture trap. The "bubble" is caused by back pressure due to a partial blockage What happens is that when you flush or drain the discharge runs down the drain line and hits the partial blockage and bounces back sending a bubble of air ahead of it. A partial blockage will also cause a backup sending soap or crud into a fixture until it can drain away.

Thank you for your reply. I assume the vent pipe is not blocked because I do not have any symptoms you described. The tenant complained about the odor in his office. I found the AAV under the sink broken. Replace it and the odor went away for about two weeks. I just replaced the toilet wax ring and the AAV again. Hopefully the smell goes away. I will keep you posted. Thanks again.

The stinky smell went away after replacing the toilet wax ring.

Thanks all for your help!