JQgrid checkbox onclick update database

You can set a click event handler inside of loadComplete:

loadComplete: function () {
    var iCol = getColumnIndexByName ($(this), 'Aktiv'), rows = this.rows, i,
        c = rows.length;

    for (i = 1; i < c; i += 1) {
        $(rows[i].cells[iCol]).click(function (e) {
            var id = $(e.target).closest('tr')[0].id,
                isChecked = $(e.target).is(':checked');
            alert('clicked on the checkbox in the row with id=' + id +
                '\nNow the checkbox is ' +
                (isChecked? 'checked': 'not checked'));
        });
    }
}

where

var getColumnIndexByName = function(grid, columnName) {
    var cm = grid.jqGrid('getGridParam', 'colModel'), i, l;
    for (i = 1, l = cm.length; i < l; i += 1) {
        if (cm[i].name === columnName) {
            return i; // return the index
        }
    }
    return -1;
};

Instead of the alert you should use jQuery.ajax to send information to the server about updating the checkbox state.

You can see a demo here.