How do I set up a knowledge base with Nintex and SharePoint 2013?
It's a wide question.
Nintex Forms could help you a lot build the different entites ( Lists ) on your Sharepoint Site, and workflows will help your to automate some actions and processes.
It depends on how you are thinking/needing your knowledge base.
There are some specific products for Sharepoint for Knowledges bases.
Make sure you understand and can explain the requirements for your knowledge base: the use cases, user roles, access restrictions, etc. Otherwise you may end up with a product designed for another scenario and the vendor will be refusing to incorporate your minority requirements as being irrelevant for the main target scenarios.
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