In the context of microservices architecture, services like User-Org-Service and Learning-Service are commonly exposed to handle specific functionalities such as user and organization management, and learning management respectively. Batch-Service, Knowledge-Service, and Certificate-Service might be part of the ecosystem but the naming convention suggests that User-Org-Service and Learning-Service are more likely to be the core services exposed by an educational platform like Sunbird Lern.

For a knowledge microservice, a combination of Neo4J, Cassandra, and Cloud Storage would provide a robust solution. Neo4J offers graph database capabilities for complex queries and relationships, Cassandra provides scalable and high-performance data management, and Cloud Storage offers a flexible solution for storing large amounts of unstructured data.

In microservices and distributed systems, caches are often used to improve performance. The command 'sync-rel-cache-all' suggests a process to synchronize and regenerate the cache for collection relationships, which is a plausible approach to constructing or reconstructing a cache in such systems.

The naming conventions used in microservices often reflect their functionality. 'questionset-service' seems most aligned with the functionality one might expect in an inquiry microservice within an educational platform, handling sets of questions or inquiries.

Apache Druid is known for its real-time analytics capabilities and is a distributed column-store data store designed for OLAP (online analytical processing) queries on event data, making it suitable for high-performance analytics.