I registered at jivesoftware.com and inthe evaluation tab there is nothing... how I can get a evaluation license ?
you may want to call Jivesoftware sales or send them an email.
Anyhow the `Enterprise Plugin´ is a discontinued product so I see little point in evaluating it. See also Openfire Enterprise End of Life FAQ.
One may ask for a cluster evaluation license as this is the only `active´ plugin which needs one.