Do you mean the internal shared-memory service request and response queues or the /Q system? If you are passing messages via the /Q system (i.e. using tpenqueue() and tpdequeue() or TMQFORWARD servers), backup is automatically because all queue messages are usually stored in a file that is created at server setup using the tmadmin tool.
As far as I know, the internal queues cannot be backed up. If the system goes down, e.g. all asynchronous request (tpacall()) that are not yet processed are lost.