Hi,
DataPin and ClockPin are both physical pins on the device, for example PortB.2 and PortD.0.
Since the SHIFTOUT command is bit-banged and software timed you can select any pins you wish as long as they can be made outputs.

The clock is generated by software loops in the PIC and sent to the pin you specify as ClockPin. You can not "drive" the SHIFTOUT or SHIFTIN commands with an external clock, with these commands it's always the PIC that generetaes the clock.

/Henrik.