Typically you would cancel a job by hitting the cancel button (red one).
If that doesn't work reboot.
Since neither of the simple methods work, I'm not sure what is left.
I can't find a reference to this device having an NVRAM reset so that is out.
If it was unplugged for a year there is no chance the job is just stuck in RAM, so booting with the RAM out is not going to help.
I don't know the formatting of the hard drive or its contents so doing anything to that would be a bad idea.
And again, because it is still there after a year, there is no chance the job is just hanging out on the LAN waiting for the device so starting it with the NIC unplugged is also a no go.
I'd suggest calling Xerox, but if there is no maintenance agreement the cost versus the issue makes sitting there feeding through the paper jams is vastly cheaper even when accounting for your pay to do so.