The proper way to SSH into a TrueNAS jail now is to SSH/WebGUISHELL into the TrueNAS box proper and switch to the jail.
First you need the ID number of the jail. You can get this from the GUI or by running…
Then run the following (replacing ## with the jail ID) to begin talking to the jail instead.
jexec ## tcsh
exit to stop talking to the jail and back to root machine.