Here I am added an image to day cell using css:
.fc-widget-content::after {
margin-top: 1 px;
margin-left: 70 px;
font-family: 'FontAwesome';content:"\f00d";
position: absolute;
white-space: pre;
color:#F00;
}
jquery, fullcalendar.js
dayClick: function(date, jsEvent, view) {
alert('Clicked on: ' + date.getDate()+"/"+date.getMonth()+"/"+date.getFullYear());
},
Yo can't do it that way. ::after is not part of the DOM so it's not accesible using Javascript.
In this answer you could find some methods to fix your problem.