Docker Again, Finding Composer Autoload

I had already tried that one.
I’ve now tried all three paths, and none are working.
The thing I’m unsure of, and this is where Docker sometimes confuses me, is whether this file should be seen (exist) on my drive. Or does it exist only within the container? Because it isn’t present on my drive, if it were I would know where it is and have a good chance at giving it the correct path.