<iframe
        id="crdamap"
        width="500"
        height="400"
        frameborder="0"
        scrolling="no"
        marginheight="0"
        marginwidth="0"
        onLoad="load_plots_for_sale();"
        title="Avenue Plots for Sale" src="https://gis.apcrda.org/lps/index.html">
      </iframe>

function load_plots_for_sale(){
    $(map).on("load", function(){
       console.log('xxxxxxxxxxxxxxxxxxxzzzzzzzzzzz');
    });
}

layer.loadend