What the information stored in backup of sepm database?
is it ability to stand a new server as running server?
all policies and client information stored in backup?
Yes all that will be included in the backup. It's so you can restore the SEPM using the backup if something goes wrong and have everything running back to normal in a short time.
Read thru this link:
Symantec Endpoint Protection 12.1: Best Practices for Disaster Recovery with the Symantec Endpoint Protection Manager
Backup contains all the info about yoru groups , policies, clients
You can restore the backup and update the keystorepassword to get clients in case of disaster recovery
Symantec Endpoint Protection Manager database contains all important data like policies, information on your clients, settings, logs, etc.
How to back up, restore, and/or move the Symantec Endpoint Protection Manager (SEPM) and embedded Database to another disk or system
https://www-secure.symantec.com/connect/articles/how-manage-sepm-121-database