Difference between junction points in old schematic
Notice that the hollow circles are only on the potentiometer connections. If the potentiometers are mounted off-board separate wires will be attached to those points.



Figure 1. Off-board potentiometer wiring example. Image source: blog.mklec.com
Guitar Effects Pedal Offboard Wiring demystified. (This seems to be offline now.)

On your PCB design I would use a pin connector symbol - maybe a pin header.