$ sudo apt-get update
$ sudo apt-get install libcgal-demo 

libcgal-demo is installed in your system.

Make ensure the libcgal-demo package were installed using the commands given below,

$ sudo dpkg-query -l | grep libcgal-demo *

You will get with libcgal-demo package name, version, architecture and description in a table

libcgal-demo package basic information: