ok let me copy paste the code from the doc for you:
const assetsManager = new BABYLON.AssetsManager(scene);
const nodeGeometryFile = assetsManager.addTextFileTask("load my node geometry", "https://yoururl.com/nodeGeometry.json");
// callback
assetsManager.onFinish = async (tasks) {
console.log("all tasks successful", tasks);
// files loaded as text need to be parsed to JSON to use
const nodeGeometryJSON = JSON.parse(nodeGeometryFile.text);
// parse json object into node geometry
const nodeGeometry = await BABYLON.NodeGeometry.Parse(nodeGeometryJSON);
}
// load all tasks
assetsManager.load();