If you are familiar with a digital Volt Meter, you can set it to AC and check the wires attached to the speaker. Since Audio is nothing more than an AC signal at different frequencies and different amplitudes, you should see the meter responding.
or, you can disconnect the speaker and use an Ohm Meter to check for resistance.
Or, you can hook another speaker up and see if you get sound.
Most likely, the speaker is blown. Very common for these to blow.
There may, or should, be a small amp mounted in there also if it is a stock speaker. You will need to check to see if the speaker is blown (resistance check) and if the amp (if it has one) is working.
Do not get one from the dealer, last time I checked, over three hundred dollars.
You can get a substitute very cheaply.
The speaker may not be wired since it's an aftermarket stereo.
You can search through some of my older post for wiring diagrams, colors to help you trace it out.
Many, Many threads here on center speaker not working, how to wire in a new speaker, etc....