http://www.trirand.com/jqgridwiki/doku.php?id=wiki%3Aoptions
multiselect: true
So it would like this..
jQuery("#list2").jqGrid({
height: 500,
width: 1000,
url:'admin/summary_server.php?t=p',
datatype: "json",
colNames:['ID', 'Project', 'Action'],
colModel:[
{name:'id',index:'id_project', width:50},
{name:'title',index:'title', width:250},
{name:'action',index:'id_project', width:250, formatter:project_actionLink}
],
rowNum:10,
rowList:[10,20,30],
editurl: 'admin/summary_server.php?t=p',
pager: jQuery('#pager2'),
sortname: 'id_project',
viewrecords: true,
***multiselect: true,
multiboxonly: true,***
sortorder: "desc",
caption:"JSON Example"
}).navGrid('#pager2',{edit:false,add:false,del:true});