I assume the link to the documentation should be easily accessible for people who want to get information on WBStack in general and for people who are logged in.

The place that makes most sense to me is in the footer with the other platform related links:

Alternatively, we could put it in the top bar but it is thematically less fitting.

Caveat: At some point we should reevaluate the footer as the "org" columns as many useful/essential links and the "community" column just links to projects generally.

Caveat 2: It is a bit irritating if the documentation lies at another place than the website.

In T308538#7934128, @Jan_Dittrich wrote:

Caveat 2: It is a bit irritating if the documentation lies at another place than the website.

I disagree; wikibase.cloud is a WMDE product, and technical documentation for our products lives on mediawiki.org. One of the most common critiques we receive is that our documentation is scattered and hard to find.

disagree; wikibase.cloud is a WMDE product, and technical documentation for our products lives on mediawiki.org

If the documentation is on Mediawiki and its internal workings: Yes, it should all be at a central place.

If it is documentation for users, much like what you got in a good old 90s application when pressing F1, I think it should ideally live on the same website or otherwise strongly signal (also visually/structurally) that one is on the help page belonging to the same project. I assumed the documentation is on stuff like adding an impressum and Administrating Wikis via WB cloud, so I assumed it will be the latter category of documentation.

Does anyone know why this task (adding a link) is taking multiple weeks? @Evelien_WMDE

It has not yet been added to the pool of tasks that engineers actively work on given there were enough of other tasks for engineers to be busy with.
So the answer to your question would be: unexpected infrastructure issues discovered on the platform that were priority before making adjustment to the site UI.

https://github.com/wbstack/ui/pull/461

After a chat with @Jan_Dittrich it was agreed to update the ordering at the same time

     Do you think the imprint link should be at the very end of the footer, or does the ordering not matter?

I would suggest:     

    About
    Documentation
    Github
    Privacy Policy
    Terms of Use
    Imprint
    Contact

To have a rough  grouping by usecase

new tag https://github.com/wbstack/ui/releases/tag/3.96

Verified, thanks.