$.ajax(
    {
        url: 'endpoint',
        method: 'GET',
        data: {
            action: 'getAgenda',
            keyuser: idLess
        },
        success: function(response){
            var dados_agenda = response;
        },
        dataType: 'json'
    }

);

{
    "id": "1",
    "title": "reuniãp",
    "start": "2019-03-19 10:00:00",
    "end": "2019-03-19 11:00:00",
    "situacao": "A",
    "cor": "#4761c5",
    "Update": "2019-03-17 16:24:00"
}{
    "id": "2",
    "title": "Churrasqueira",
    "start": "2019-03-20 10:00:00",
    "end": "2019-03-20 11:00:00",
    "situacao": "A",
    "cor": "#4761c5",
    "Update": "2019-03-17 18:17:00"
}

$(document).ready(function() {

   $('#calendar').fullCalendar({
     header: {
       left: 'prev,next today',
       center: 'title',
       right: 'month,basicWeek,basicDay'
     },
     defaultDate: '2019-03-12',
     navLinks: true,
     editable: true,
     eventLimit: true,
     events:[
    {
      id: 999,                     <- id entrar aqui
      title: 'All Day Event',      <- title entrar aqui
      start: '2019-01-01',         <- start entrar aqui
      end: '2019-03-07'            <- end entrar aqui
    },
    {
      id: 999,                     <- id entrar aqui
      title: 'Long Event',         <- title entrar aqui
      start: '2019-03-07',         <- start entrar aqui
      end: '2019-03-07'            <- end entrar aqui
    }
  ]

   });
});

$('#calendar').fullCalendar('addEventSource', dados_agenda );