You can do this:
JSON.parse('{"response":[{"job_id":"29","message":"egfn","lattitude":"26.9514731","longitude":"89.4524783","job_status":"P","date":"2013-11-21 03:33:34","username":"users"},{"job_id":"28","message":"egfn","lattitude":"26.9514731","longitude":"89.4524783","job_status":"P","date":"2013-11-21 03:33:34","username":"rajeev"},{"job_id":"27","message":"egfn","lattitude":"26.9514731","longitude":"89.4524783","job_status":"P","date":"2013-11-21 03:33:34","username":"pankaj"},{"job_id":"26","message":"test job for you","lattitude":"25.4558641","longitude":"80.1325838","job_status":"P","date":"2013-11-21 01:09:58","username":"users"},{"job_id":"24","message":"test job for you","lattitude":"25.4558641","longitude":"80.1325838","job_status":"D","date":"2013-11-21 01:09:58","username":"amit"},{"job_id":"25","message":"test job for you","lattitude":"25.4558641","longitude":"80.1325838","job_status":"P","date":"2013-11-21 01:09:58","username":"test"}]}')
EDIT:
to get all job_id do this:
var obj = JSON.parse('{"response":[{"job_id":"29","message":"egfn","lattitude":"26.9514731","longitude":"89.4524783","job_status":"P","date":"2013-11-21 03:33:34","username":"users"},{"job_id":"28","message":"egfn","lattitude":"26.9514731","longitude":"89.4524783","job_status":"P","date":"2013-11-21 03:33:34","username":"rajeev"},{"job_id":"27","message":"egfn","lattitude":"26.9514731","longitude":"89.4524783","job_status":"P","date":"2013-11-21 03:33:34","username":"pankaj"},{"job_id":"26","message":"test job for you","lattitude":"25.4558641","longitude":"80.1325838","job_status":"P","date":"2013-11-21 01:09:58","username":"users"},{"job_id":"24","message":"test job for you","lattitude":"25.4558641","longitude":"80.1325838","job_status":"D","date":"2013-11-21 01:09:58","username":"amit"},{"job_id":"25","message":"test job for you","lattitude":"25.4558641","longitude":"80.1325838","job_status":"P","date":"2013-11-21 01:09:58","username":"test"}]}')
var job_id_array = new Array();
for(var i = 0;i< obj.response.length ; i++){
job_id_array.push(obj.response[i].job_id);
}