How to connect two FPGA boards - VHDL
Use PORT A.  Use an I/O pin for receiving, an other I/O pin for sending and a ground.  This requires three wires.  You cross the cables for the I/Os to that the "send" pin connects to the "receive" pin of the other board and reverse.  This allows to have two identical "code"/"schematic" on both board.

For project proposal, you can use switches and buttons to allow encoding a short message on display and then you send the message.  The other board receives the message and display on the display.  You could have up to 8 char or more an scroll.  As you see fit.  Nothing very hard to do and possibly quite fun for a small university project.