This plugin allows you to ping an entity.
Usage (globally): /ping <jid>
Usage (in a MUC tab): /ping <jid or nick>
Usage (in a conversation tab): /ping [jid]
Globally, you can do /ping jid@example.com to get a ping.
In a MUC, you can either do it to a JID or a nick (/ping nick or /ping jid@example.com).
In a private or a direct conversation, you can do /ping to ping the current interlocutor.