You do not see this is NetBackup, this is at an operating system level / cluster software level. For example, for a Veritas cluster you can run the command: hastatus

Editted to add ...

... apart from nbemmcmd

Please tell us which NBU version and OS on your Master server cluster nodes as well which Clustering software.

'nbemmcmd -listhosts -verbose' should help if NBU was correctly installed as clustered master.

Output similar to the following:

server          virtual-name
cluster         virtual-name
......
master          nodename1
master          nodename2

NBU version: 7.1.0.2

os:Linux

You forgot to mention which clustering software is used...

Have you checked output of 'nbemmcmd -listhosts' yet?