I apologize that the details are not provided in the user manual yet. I should add them soon. OSPi 1.4 uses the first 8 pins on the 3.3V column (same as the 8 pins you see in the picture you attached), and the first 5 pins on the 5V column. On the circuit board you can see that the occupied pins are surrounded by a white box in the silkscreen. They are pretty subtle but should be visible. The other pins are free to use. Also, the SDA/SCL pins (which OSPi 1.4 uses for RTC and ADC) can be shared with other devices.