Hi @KurtE.
This is J5:
https://docs.arduino.cc/resources/schematics/ASX00021-schematics.pdf
Even though it has 40 pins, the 2-1734248-0 connector is only 20p, so this is why only 20 pins are shown in the schematic even though there are 40 pads on the board (the row of pads closest to the edge of the board are not connected to any net, only serving a mechanical purpose).