am replacing the NEC Electra Elite IPK B64-U30 phone system, can anyone tell me what the card inside the system that has 2 8-conductor plugs connected to it does? It is in the S2 slot.

Can you read the card type on the edge of the card? Is the card you are referring to "piggy-backed" onto another card (say an ESI-B (8) ?). If so it will the 8-port daughter board for the station card, giving you a total of 16 ports in that slot.

I do have a picture of interior of cabinet if that would help, I cannot tell for sure if this is a daughterboard--thanks

It is most likely either an analog or digital station card with a daughter board.