find all unchecked checkbox in jquery

As the error message states, jQuery does not include a :unchecked selector.
Instead, you need to invert the :checked selector:

$("input:checkbox:not(:checked)")

$("input:checkbox:not(:checked)") Will get you the unchecked boxes.

You can do so by extending jQuerys functionality. This will shorten the amount of text you have to write for the selector.

$.extend($.expr[':'], {
        unchecked: function (obj) {
            return ((obj.type == 'checkbox' || obj.type == 'radio') && !$(obj).is(':checked'));
        }
    }
);

You can then use $("input:unchecked") to get all checkboxes and radio buttons that are checked.