I tried to look at the main documentation at http://graphics.pixar.com/usd/docs/index.html and http://graphics.pixar.com/usd/docs/Usdz-File-Format-Specification.html but cou
Assuming that you're on macOS, since you're trying to create USDZ files, then Apple released Reality Converter (currently Beta) in January of this year (2020). It allows you to drag and drop OBJ files and export to USDZ.