$ sudo apt-get update
$ sudo apt-get install google-sitemapgen 

google-sitemapgen is installed in your system.

Make ensure the google-sitemapgen package were installed using the commands given below,

$ sudo dpkg-query -l | grep google-sitemapgen *

You will get with google-sitemapgen package name, version, architecture and description in a table

google-sitemapgen package basic information: