Marc,
You can get the graphics from the layers view:
// Carbon storage of trees in Warren Wilson College.
var featureLayer = new FeatureLayer({
url: "https://services.arcgis.com/V6ZHFr6zdgNZuVG0/arcgis/rest/services/Landscape_Trees/FeatureServer/0"
});
featureLayer.on("layer-view-create", function(evt){
//The LayerView for the layer that emitted this event
console.info(evt.layerView);
});
The layerView has a graphics property.
But be aware of this note in the docs:
In this version of the API, geometries and attributes of features in a FeatureLayer cannot be added, deleted, or edited.