DE2-115 schematics don't show EPCS pins

The EPCS device pins are fixed, i.e., you have no choice as to their pin assignments. The EPCS device is used for Active Serial (AS) configuration, and then once the FPGA enters user-mode, you can access the EPCS device as user SPI flash. If you add the Altera EPCS flash IP core into your design, eg., Qsys, I don't think you need to make any pin assignments, otherwise you can just look at the pin planner view and note which pins correspond to the AS pins and use those in your assignments. Sometimes the Terasic schematics do not show the configuration device page (since it also includes the USB-Blaster circuit).