With the Android version of Jitsi, I can't find any way to view a
contact's details, so all I can see is the Alias I've given it (or
maybe it was automatically set from the server) and no way to view the
actual address (i.e. firstname.lastname@example.org) that it's associated with.
Long-press just gives me "Remove contact".
On Windows Jitsi, we've got right-click on a contact but in fact that
doesn't appear to offer a way to view this information, as if I rename
a contact from email@example.com to example, then this is all that's
displayed on right-click Contact Info and even under Security - Chat,
where it shows the fingerprints.