Having permission to view the presence status of a person is called subscribing to his presence. Presence subscription between two persons can be asymmetric.
When jabber.el receives a presence subscription request, it will present it to you in an alert requiring immediate response, and offer you to send a subscription request back to that person.
To request subscription to someone, type M-x
jabber-send-subscription-request. You will be prompted for the JID
to send it to. This command can also be accessed through the Roster
menu, by typing C-c C-r in the roster buffer. After that, you
will probably want to give the contact a more readable name. The
command for that is jabber-roster-change, which is also
available in the Roster menu or by typing e on a person in the
roster buffer.