I created an example of a NET Core Web Api that makes use of both the Cosmos DB SDK 2.0 and 3.0.
The example is based on an Order entity with multiple Order Item entities. It includes controller methods for working with Orders in both v1 and v2 of the API. Note, in v2 of the Api, I included controller methods for working with Order Items individually.
The repository can be found at https://github.com/mattruma/CosmosDBWebApi.