Yes, you can add point, line, and polygon graphics client side using the Javascript API. Here is an example of how to add a point graphic:
require([
"esri/Map",
"esri/views/MapView",
"esri/Graphic",
"esri/layers/GraphicsLayer"
], function(Map, MapView, Graphic, GraphicsLayer) {
var graphicsLayer = new GraphicsLayer();
map.add(graphicsLayer);
var point = { type: "point", longitude: -118.80657463861, latitude: 34.0005930608889 };
var simpleMarkerSymbol = { type: "simple-marker", color: [226, 119, 40],
var pointGraphic = new Graphic({ geometry: point, symbol: simpleMarkerSymbol });
graphicsLayer.add(pointGraphic);
}
Source: Display point, line, and polygon graphics | ArcGIS for Developers