To view the list of disks lent to particular user, you need to
open the contact list, select the user. Lent volumes will be
displayed in the bottom part of the Contact list. Use the context
menu to edit disks in the contact list.
Also the lent disks are marked with a special icon (hand, see
screenshot). The username is displayed in the "Lent to" column in
the right panel of the main window.