dayClick
Triggered when the user clicks on a day.
function( date, allDay, jsEvent, view ) { }
date holds a Date object for the current day. If user has clicked on a slot in the agendaWeek or agendaDay views, date will also have its time set.
allDay will be set to false if the user has clicked on a slot in the agendaWeek or agendaDay views. Otherwise, it will be true.
jsEvent holds the native JavaScript event with low-level information such as click coordinates.
view is set to the current View Object.
Within the callback function, this is set to the <td> of the clicked day.
Here is an example that demonstrates all of these variables:
$('#calendar').fullCalendar({
  dayClick: function(date, allDay, jsEvent, view) {
    if (allDay) {
      alert('Clicked on the entire day: ' + date);
    }else{
      alert('Clicked on the slot: ' + date);
    }
    alert('Coordinates: ' + jsEvent.pageX + ',' + jsEvent.pageY);
    alert('Current view: ' + view.name);
    // change the day's background color just for fun
    $(this).css('background-color', 'red');
  }
});
The allDay parameter has only been available since version 1.4.