Work item wiki is a control to render a wikipage inside a work item page. This can be useful if you need to document something for that work item type. For example definition of done/ready, bug categories etc.
Work Item Link is a custom form control that needs to be added to the Work Item Form. It can be added on an existing page, or as a new tab. For how to do this, refer to the official documentation.
Wiki Url is the url to the wiki page, it should look something like: https://dev.azure.com/organization/demo-project/_wiki/wikis/demo-project.wiki/1/This-is-a-page
Version Branch is used when publishing the wiki from code. If your main branch is not wikiMaster, this field must be set to load links, images and attachments correctly.