Hi Sarah,
A useful command for this is:
>show virtual chassis vc port
In example:
show virtual-chassis vc-path source-interface ge-0/0/0 destination-interface ge-0/0/43
will give you this output (this can also be done across VC members):
vc-path from ge-0/0/0 to ge-0/0/43
Hop Member PFE-Device Interface
0 0 1 ge-0/0/0
1 0 2 internal-1/25
2 0 0 ge-0/0/43
As you can see here it is telling you
ge-0/0/0 is an interface from PFE-Dev 1
ge-0/0/43 is an interface from PFE-Dev 0
and PFE-Dev 2 is actually internal (internal-1/25 is actually part of the VC-ports)
you can experiment a little with that command I am sure you can see the information you need that way.
Regards!