I second the vote for the Etihad lounge, though it has been over a year since I last used it, and with Etihad on their cost-cutting spree, I don't know what the level of service at the lounge is at now.
There isn't a separate Jet transit desk, afaik, but if you get into terminal 2C on the bus from 2A, there's a general assistance desk in the lobby just as you get off, who are usually able to help with queries.