I have started jboss and send it to background process from a particular ssh session. But as the session got timeout I did ssh (diff session) but now neither I could list the bg jobs nor jobs command returns anything.
jobs are only for jobs started by the current shell. Since you got a new shell when connecting again, it cannot see the jobs of the previous one.
It is also possible that your bash session got killed by the disconnect, which in turn killed its background jobs. If you want your background jobs to survive this kind of accident, start them with