Okay, I see, but I am currently using the @ArcGIS/core library. Even when I try to find the module, I get an error that it can't be found. I see that there is not a module named 'panel' inside the 'chunks' directory.
require(['@arcgis/chunks/panel'], function (panel) {
panel.Panel.prototype.renderHeaderNode = function () {
return null;
};
});