You can create a knowledge base in any workgroup or project.
Enable this feature when creating a new workgroup/project or when editing the existing one:
Then click the Knowledge base button:
Select a template, specify the knowledge base name and description, and select a color theme:
You're all set to add and edit the knowledge base pages.
Any member of the workgroup/project can edit its knowledge base.
You can create only one knowledge base for each workgroup or project. The number of workgroups/projects you can create is unlimited regardless of your Bitrix24 plan.