Where to wire usb shield output on breakout
If you are trying to replace the USB cable with with the USB C port, then you would simply connect the S pin to the shield of the USB C connector by literally connecting a jumper wire from the S pin to any one of the four shield pins on the bottom(or top, being careful not to let the solder spread away from the bottom of the connector) of the USB C adapter PCB:



If you are trying to add a USB C "accessory" port to your standard USB keyboard, then active USB hub circuitry will be required, either by designing your own circuit board, or salvaging the circuit board from a donor USB hub and wiring it between the USB-to-host cable, the keyboard circuitry, and the USB C "accessory" port.  You should keep in mind, however, that this configuration is not officially supported by the USB C specification, and may or may not work depending on the hardware, and would also likely require the removal of the two resistors on the USB C board.