Hello Ravi,
In the knowledge project, you will store only documents. It could be your knowledge library. You can create different knowledge projects by topic, subjects...
It supports shortcut from/to these workspaces.
The Sourcing project enables you to create all your projects for sourcing. In theses projects you will we able to have your event sourcing with eRFI, eAuction, eRfq, eRFp. And beeing able to have some tasks workflow to drive your sourcing project.
You can also store some documents to support your sourcing projects.
Hope that will help you