Edit in JSFiddle

function viewModel() {
    var self = this;
    self.subject = ko.observableArray(["Phy", "Che", "Bio"]),
    self.removeSubject = function (data, event) {
        if (event.shiftKey) {
            self.subject.remove(data);
        }
    }
}
ko.applyBindings(new viewModel());

<ul data-bind="foreach: subject">
    <li> <span data-bind="text: $data"></span>

        <button data-bind="click: $parent.removeSubject">Remove</button>
    </li>
</ul>