Do you have some ID for the building you want to highlight? If so, the easiest way would be to use the 3D Tiles styling language, to highlight the building:If you want to do a post processing feature like here: https://sandcastle.cesium.com/index.html?src=3D%20Tiles%20Feature%20Picking.html
You would need some way to get access to the Cesium3DTileFeature, which would involve iterating over all the tiles in view as discussed here:
Let me know which approach works for you.