Service discovery is used to find information about servers, services and clients. There are two kinds of requests: find info about a Jabber entity—i.e. its identity and supported features—and find items related to an entity, where the definition of “related” is left to the entity itself.
The commands to execute such requests are
jabber-get-disco-items, respectively. These commands can be
accessed from the Info menu, which is opened by typing C-c C-i.
The commands accept a JID and optionally a “node”.
The result of such a command is displayed in a browse buffer. For an info request, the result just lists the identities and features of the entity. For an item request, the related items are listed. The items may be JIDs, or JIDs with a node. If you put point on one of the items, its JID and node will be the default value for any Jabber command.
If you think that the interface to service discovery is awkward and should be replaced with something better, you are completely right.