You're closing it with a semicolon. You want a comma
$("#responds").sortable({
axis: 'y',
update: function(event, ui) {
var data = $(this).sortable('serialize');
$.ajax({
type : 'POST',
url : 'process.php',
data : {position: data},
dataType : "html",
success : function(data) {
alert("hej");
},
error : function(xhr, ajaxOptions, thrownError) {
alert(thrownError);
}
});
}
});