$ sudo apt-get update
$ sudo apt-get install libcgns2 

libcgns2 is installed in your system.

Make ensure the libcgns2 package were installed using the commands given below,

$ sudo dpkg-query -l | grep libcgns2 *

You will get with libcgns2 package name, version, architecture and description in a table

libcgns2 package basic information: