Are you using the default NCP target example? It configures the USART0 (PA0/PA1/PA2/PA3) straight connect to the VCOM as the default communication port. You can modify the UART configuration to route the TX/RX/CTS/RTS and wake pins to the required pins, see the "4.1.1 UART Configuration" of AN1042 for more information.
For the pins are not present on the Expansion Header, you can connect the NCP host to the EFR32MG12 via the breakout ports directly. Please don't forget to disable the VCOM to disable forwarding the NCP communication to the J-Link CDC Virtual COM port on the WSTK.
Here, trying to pick this up where I left it off after long time of inactivity on the subject
I am using the NCP target example. On Client side I am using project "ncp-empty-target". I have my custom device connected to Expantion header pins 12/14 (TX\RX respectivly according to BRD4001A schematic) while powerd by USB from PC. I would very much like to work through WSTK for debugging \ tracing purposes.
I am trubled with like this which seem to have been left unresolved:
And others that I am not sure relate:
I have tried disabling the VCOM. Any specific configuration you can provide?