Update: I confirm it works!
Steps,
1. download the ColVis extra from here, http://www.datatables.net/extras/
2. paste the extra under assets/grocery_crud/themes/datatables/extras
3. rename the folder to ColVis
4. under assets/grocery_crud/themes/datatables/js open the file datatables.js and replace
this line : "sDom": 'T<"clear"><"H"lfr>t<"F"ip>',
with this : "sDom": 'CT<"clear"><"H"lfr>t<"F"ip>',
5. under assets/grocery_crud/themes/datatables/views open the file list_template.php and add these two lines at the top
$this->set_css($this->default_theme_path.'/datatables/extras/ColVis/media/css/ColVis.css');
$this->set_js($this->default_theme_path.'/datatables/extras/ColVis/media/js/ColVis.min.js');
so it looks like this
6. Enjoy! http://eletter.gr/samples/gc_ic/index.php/gc_examples/employees_management