Hi, feathers have default pins for SPI communication, you should use those (SCK and MOSI in this case), other pins are normally any pins you choose as long as you set it up correctly in the software then by matching the pins. It should be like that, using the markings on the silkscreen:
Feather -> Display
GND -> GND (G)
3.3v -> VIN (+)
SCK -> SCLK (CL)
MO -> MOSI (SI)
MI -> MISO (SO)
any -> DC
any -> OLEDCS (OC)
any -> RST (R)
OC/OLEDCS is the CS (chip select) pin for the display.
To use the SD Card you also need to setup the Chip Select pin for the SD card, SDCS (or SC), to any pin.
Here is a wiring diagram for another display that uses pins D6, D9 and D10 for the free pins:
https://learn.adafruit.com/2-2-tft-display/circuitpython-displayio-quickstart#wiring-the-breakout-to-the-feather-3037059