What is the difference between knowledge base space and documentation space ?

[Santosh Kumar Alajangi]

We need exact difference between Different types of space templates ?

[Kishan Sharma · Accepted solution]

Welcome to the Atlassian Community @Santosh Kumar Alajangi 
The difference is just the structure of the space templates.

A knowledge base is a repository for how-to and troubleshooting information. Knowledge Bases are commonly used by IT Support teams, but can be useful for procedural and troubleshooting information in any organization or team. Its generally used as self-help support to customers and integrated with Jira Service Management.

'Documentation Space' will give you a custom home page with a search box (the livesearch macro) to search just your documentation space. 

However you can combine features of both irrespective of which space template do you use.

You can refer Use Confluence as a Knowledge Base and Develop Technical Documentation in Confluence for more detailed documentation.