Isolate by swapping. No tools, no multimeter, and in three steps you will know whether it is the speaker, the wire or the AVR channel.
First, the AVR's built-in test tone. Run it and listen. If the suspect speaker plays the test tone but stays silent on films, the fault is not physical: it is a level trim set to minimum, a speaker set to "None" in configuration, or a source that simply does not carry that channel. If it is silent on the test tone too, the fault is real and we go to step two.
Second, at the AVR, swap the suspect speaker's wire with a working channel's wire. Suppose the left surround is dead: connect its wire to the right surround terminals and vice versa. Run the test tone again. If the dead speaker now plays, the AVR channel or its amp assignment is the problem. If the same speaker stays dead in its new home, the AVR is innocent and the fault is in the wire or the speaker.
Third, take the suspect speaker to the AVR and connect it directly to a known-good channel with a short length of fresh wire. If it plays, the long run in the wall or under the carpet is damaged somewhere. If it stays silent, the speaker itself needs service. Drivers do fail, and a voice coil that has been overdriven does not announce it politely.
One caution I would take seriously. If the channel died with a distorted crackle at high volume, stop testing and get it looked at. That crackle is usually a damaged driver or a stressed amplifier stage, and continuing to drive it, even at test-tone level, can turn a small repair into a big one. Curiosity is expensive at that point.
Cable faults, incidentally, are the most common answer we find, especially on in-wall runs done during construction where a nail or a bent staple did its work quietly. If you reach that conclusion, tell us the run length and I will suggest how to test and replace it without opening the whole wall.
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