Hi @kevinang86,

Thanks for your question! Have you already taken a look at this tutorial on Uploading Assets to Cesium ion? This example includes a downloadable workspace that shows the workflow as well. Since you have your data in CityGML already, the CesiumIonConnector may be the easiest method. This is the same one demo'd in the tutorial.

An alternative method is to use the Cesium 3D Tiles Writer. I would try starting with your CityGML reader straight to the writer first and see if it outputs everything you want and as expected before making any additions. The translation log will usually give you actionable hints if you hit any snags in the translation.

Hope that helps!