To style data with OGC SLD/SE styling definitions, use the factory methods in the SEPainterFactory module to create a FeaturePainter. You can use that FeaturePainter just like any other FeaturePainter implementation, and install it on a FeatureLayer:

//Use the factory method from the SEPainterFactory module to create the painter
//As input we use the url of the SLD file
const seURL = "http://foo.com/se/CitiesSymbolizer.xml";
createPainterFromURL(seURL)
    .then(function(sePainter) {
          //Create a new layer which uses the created painter
          const layer = new FeatureLayer(citiesModel, {
            label: "Cities Layer",
            painter: sePainter
          });
          //Add the layer to the map
          map.layerTree.addChild(layer);
        },
        function(error) {
          console.log("could not create a painter from symbology encoding at " + seURL);
        }
    );