For a bit more info, are you wanting to physically detach the shelf from one filer (or filer pair) and move it to another filer (or filer pair)? Or is the shelf assigned to one partner and you want it assigned to the other?
You can see which disks are part of an aggregate using sysconfig -r or aggr status -r. If the disks are assigned to a filer but not in an aggregate, they should be listed as spares (aggr status -s). If they aren't assgined to a filer, you can see them using disk show -n.
Do you want to remove physically from one HA pair to another HA pair? If you want to remove physically, you need to remove ownership of all the disk from the shelf that you want to move else the filer will complain about missing disk and panic. You may use disk remove_ownership command to remove ownership. Before removing ownership, make sure the disks are not in-used in any aggregate. You can check with sysconfig -r, aggr status command for raid group and aggregate information and you can use vol status -s command to check the spares disk. use disk show -n to see all the unassigned disk.