The column name is "Dialog Box". I tried this
var context = new SP.ClientContext.get_current();
var targetList = context.get_web().get_lists().getByTitle("myList");
var targetListItem = targetList.getItemById(_spGetQueryParam('id'));
context.load(targetListItem, "Dialog Box");
context.executeQueryAsync(Function.createDelegate(this, onStatusQuerySucceeded), Function.createDelegate(this, onStatusQueryFailed));
function onStatusQuerySucceeded() {
alert(targetListItem.get_item("Dialog Box"));
}
function onStatusQueryFailed(sender, args) {
alert("failed Dialog Box");
}