Two approaches I've used for that:

1. Having a "doc of docs" for each team - a document (Google Doc, wiki page, whatever) that acts as an index for all of the other documentation. If anyone asks "where's the documentation for X?" the answer should be "It's in the doc-of-docs. And if it isn't, it's your job to find it and put a link to it in the doc-of-docs".

2. Get a good search engine! I built a search engine for work that indexed documentation content from 8 different sources, because building a single search index was easier than convincing dozens of teams to switch the documentation solution they were using. I used an improved variant of the technique I described in https://24ways.org/2018/fast-autocomplete-search-for-your-we...