There's the jig:


The N950 sits locked on top, with the battery removed. The battery can be placed on the back of the jig or an external PSU can be used, see bottom left corner.
Normally the UART is connected to the computer with the RS232 terminal via a DB9-to-RJ50 cable (which contains a RS232 level adapter) to the 10pins UART connector to the left, but by using the switch on the top left corner, the DB9 on the jig can instead be selected.

The chip sitting behind the DB9 connector is a MAX3218, a common RS232 transceiver / level adapter.
So, if the DB9 connector is selected, there is electrical continuity:
- between pin10 of the max3218 (R2OUT) and the 2nd pin (counting from left) on the top row of pogopins. The corresponding R2IN signal goes to pin 2 of the DB9 (RXD)
- between pin 8 of the max3218 (T2IN) and the 1st pin on the left on the bottom row of pogopins. The corresponding T2OUT goes to pin 3 of the DB9 (TXD)
- 2nd pin from left on the bottom row offers a handy GND.
Didn't trace the other signals as after all TXD, RXD and GND are probably all what matters
Serial communications works at 115200 8N1, and under Harmattan the serial terminal is seen as ttyS0.