That's also correct: no potentiometer is going to be no sound. If the pot is placed (and not broken, wrong type, or turned all the way down), there should be some sound, even without any patch wire (in fact, I also didn't see one in the schematic -there's a dotted line between the two pots shown there, but that just suggests to me that the two pots shown there are driven together as one - that line also doesn't run to any pin of the pot, unless I'm totally cross-eyed now 😁).
As I understood Klench, he does have the pot installed, but is missing the knob and was wondering about the patch-wire that can be seen it the picture in the first post.
As for the latest question: Without the knob, the alps pot I got for this is indeed a bit difficult to adjust as it's threaded for a screw. Even just using some washers under the screw might simply block it. It might work just tightening the screw and trying to carefully turn it afterwards by the screw (which is what I did, before I printed the knob) - after all, when it's set once and with using external speakers, there's usually not much need to touch it again.
The better way would probably be to find someone with a 3D printer and having them print the part for you - it's a small thing with no big associated costs.
Maybe, if you'd want to hint where you're from, someone could also help you out with it. As long as it's not international shipping, I wouldn't mind sending you one.
Otherwise, you could let e.g. JLCPCB print one for you - the part itself is going to be 1 USD and with shipping, etc. it might come up to about 5 or 6 USD (unless you have more things to order).