A good first section for a simple consumer would be creating a consumer that reads the ACK data from the topic and executes the same code (e.g. calling the service), like in here:

https://github.com/aerogear/aerogear-unifiedpush-server/blob/GSOC_2017_kafka/jaxrs/src/main/java/org/jboss/aerogear/unifiedpush/rest/registry/installations/InstallationRegistrationEndpoint.java#L230