SS, also known as CS or "chip select" can be any available digital pin, and you can communicate with several SPI components by having each connected to a different pin for CS and having software pull one down to activate that component and pull the others up to disactivate the others. All SPI devices share the same pins for the other 3. Do read through the documentation for the Nano and for your display board, and work through the sample programs. There are other shields around that have 2 SPI links, e.g. a CAN shield that also has a micro card slot, and there's lots of documentation and examples for that.
Ciao,
Lenny