Where can I find sample forms for select one from GeoJSON?

May I have this XLSForm and its related GeoJSON file to learn more detail?

Thank you in advance.

There are various sample forms linked from this post. There is also documentation here. Have you tried those sample forms? Do you have specific questions about them?

Please note that there is no advantage to using GeoJSON over CSV or internal choice lists so you should use whichever is most convenient for you. In particular, I would only recommend using GeoJSON if you already have some process or tool that provides GeoJSON or a format that is easily converted to GeoJSON. If you're using data previously gathered with ODK, for example, attaching a CSV will be much more convenient.