use Data models
All the data models available in Github under the umbrella repository smart-data-models are free to use and with an open license allowing its modification. You have a list here.
There are examples in all of them in several formats, including json, jsonld, dtdl and csv.
Additionally, there are schemas that help you to check the validity of the json payloads (for key values formats).
All these data models work on NGSI compliant platforms like the FIWARE platform but they can be used in any other.