The page on mw.org is API:Licensing.
ricordisamoa> BTW what license are API data released under? Nothing at https://meta.wikimedia.org/wiki/Research:Data#Access_2 or https://meta.wikimedia.org/wiki/Research:Data/FAQ
ricordisamoa> corporate users will want to know
qgil> ricordisamoa, the license of "API data" is the same as the license of the equivalent content?
anomie> ricordisamoa: Off the top of my head, the parts of the (action) API response that have actual content is the license of that content. Auto-generated documentation is probably under the terms of MediaWiki and/or the extensions providing the messages. Most of the rest is probably not rising to the level of copyright protection. But ask a lawyer if you really want to know.
ricordisamoa> anomie: I don't care, but someone else might
ricordisamoa> eg, is attribution mandatory when aggregating usercontribs data?
spagewmf> there's a phab task for incorporating license information
(^I thought we had a task for this but couldn't find it, et voici.)
So we need an API page about licensing that answers the basic question "What's the license of the free open knowledge I'm getting?". To answer the question, perhaps the meta query for the siteprop rightsinfo (sample) tells you the license of the data, though bugs like T112606: [Bug] The API query for rightsinfo on www.wikidata.org reports CC-SA 3.0 , while its page footer says CC0 as well.
The wiki page can mention some of these wrinkles as well
- the generated API help for a module shows the license of the module's source code as "License" (sample).
- The "licensing" discussion in T312#1107217 onwards seems more about generated documentation.
- T104288: Blueprint skin has no footer or replacement (so no copyright)