The 2x5 header that is exposed is P1 and is shown on page 22 of the datasheet. This dongle only provides 5V on pin 8. The target device should provide its I/O voltage to pin 4 (VTREF) of the dongle. VTREF sets the voltage of the ‘B’ side of level shifters 1 and 2 also shown on page 22. This lets the dongle know what voltage to drive the comm pins.