The register
The register lists Wikimedia UK in London as a licensed sponsor on Skilled Worker, an entry that goes back to at least 2026. Rating on the current register: Worker (A rating).
Companies House lists it as Wikimedia UK, number 06741827, incorporated 2008: 17 years of filings behind the name. The registered office is at Wikimedia Uk C/O The British Library 96 Euston Road, Level 4, Room 46018, London, NW1 2DB, NW1 2DB. By its SIC codes the business is in other services. It has traded under other names before, including Wikimedia U.K., Wiki UK Limited.
A licence says an organisation may sponsor; it does not say it is hiring today. The way to find out is the same as for any employer: the careers page, the job boards, and a direct approach with a UK-style CV that says early that sponsorship would be needed.