AnimatedModel.play?

Check the content of your .js files because this code works (only changed the script src targets:

<html>

<head>
    <meta charset="UTF-8">
    <title>Show Inspector</title>
    <style type="text/css">
        html,
        body {
            margin: 0;
            padding: 0;
            width: 100%;
            height: 100%;
            overflow: hidden;
            background-color: #000000;
        }

        #my_canvas {
            width: 100%;
            height: 100%;
            touch-action: none;
        }
    </style>

    <script src="https://preview.babylonjs.com/babylon.js"></script>
    <script src="https://preview.babylonjs.com/inspector/babylon.inspector.bundle.js"></script>

    <script>
        var canvas_id; var engine; var scene; var camera; var light;

        function init() {
            setup_Babylon_Scene();
        }

        function setup_Babylon_Scene() {
            canvas_id = document.getElementById("my_canvas");
            engine = new BABYLON.Engine(canvas_id, true);
            scene = new BABYLON.Scene(engine);

            camera = new BABYLON.ArcRotateCamera("Camera1", 0, 0, 5, BABYLON.Vector3.Zero(), scene);
            camera.attachControl(canvas_id); //Default controls enabled.

            light = new BABYLON.PointLight("Light1", new BABYLON.Vector3(-20, 30, -20), scene);

            BABYLON.SceneLoader.ImportMesh("", "", "skinned_model.babylon", scene, model_1_completed);

            engine.runRenderLoop(onEnterFrame);
            window.addEventListener("resize", function() { engine.resize(); });
            scene.debugLayer.show();
        }

        function model_1_completed(newMeshes, particleSystems, skeletons) {
            console.log("Model_Loaded");
        }

        function onEnterFrame() {
            scene.render();

        }
    </script>
</head>

<body onLoad="init()">
    <canvas id="my_canvas"></canvas>
</body>

</html>