How to get featureId in EXT_mesh_features

I have points cloud tileset(3D Tiles Next). There are two featureIds(Feature ID by Vertex) in each tile.
In Sandcastle, I can’t get the feaureId of the selected feature.
I can’t even get Cesium3DTileFeature. Picking result is something else.

So how to get featureid? I want to use this id to get properties from database.