What the line carries
The F39-JC10B: Mechanically it is a paired leadset, not a single jumper — both ends of the run ship together so the expansion chassis sits at the distance the cabinet layout needs rather than being shoehorned against the CPU backplane.
Where it sits in the panel
Function class is PLC expansion interconnect: the cable routes the expansion bus from the CPU or base unit out to a remote expansion chassis for distributed PLC I/O.