https://i.imgur.com/tMkey.png

It can't be bulb, I just got this car, it was working fine before.

 

When a bulb is not working you two items have to be available at the bulb connector. 12V on on wire and ground on the other. I would unplug the non-working bulb, turn on the tail lights and see if you have 12V to ground on the non-black wire and ~ zero resistance to ground on the black wire. Find a bare metal bolt to use as your ground.

I am not familiar with the 6th gen tail light setup. Is this just the tail lights? Do the brake lights work?

 

brake lights (the one in the picture that I say work) work, but the tail light (the trunk part) does NOT work. it just happened all of a sudden, I don't know how to go about fixing this problem.

 

A volt meter will help figure out what side of the circuit is not working. Once you know what is missing, you can work backwards to find the cause.

 

So this is a wire problem? Let's say I were to check with a volt meter, and find the wire with no volts. replace wires?

 

I don't know the problem. First do the tests that I suggested. Once you do those tests, post the results on here. Then you can go on to the next logical place to test.

 

Why can't it be a burned out bulb?
It seems unlikely that both sides would burn out, but not impossible.

When you are not pressing on the brakes, do the outboard tail lights work? Those are the other circuit in the "brake light" bulbs (the dimmer of the 2 filaments). How about the side marker lights? Parking lights in front?