Hello Abhishek
It seems that this command is not available in your IOS version. You can see from the following Cisco CLI reference, that the command was introduced in the T train of code and not in the mainline which is your IOS version.
Even so, this is simply a show command that conveniently displays the components of the topology. You can still obtain the same information with a variety of other show commands such as those indicated in the following Cisco document:
Note this document was published before the introduction of of the show dmvpn command.
I hope this has been helpful!
Laz