Creating read views involves consuming one or more of the projection topics and writing them to a database suitable for querying.
This is out of scope for Simple Sourcing, and it is up to the client to decide how to do this.
The recommended option is to use Kafka Streams directly to do the desired transformation and aggregation either from the event stream or the aggregate topic to new projection topics. Then use Kafka Connect to stream the output of these topics to a database or search/query engine of your choice.
In the example app (examples/auction) we have provided an example of writing the projection topics to MongoDB
using the Kafka Connect MongoDB sink
Please take a look at the example for more details.