It's very far from all the humanity's accumulated knowledge. Wikipedia is but a digest of of the deeper end of science, and barely scratches the applied sciences that are required for the modern advanced technology.

To preserve a copy of the humanity's recorded knowledge, you'd have to keep a copy of the library of Congress + archives of all scientific journals + arxiv.org, and equivalents of it for other languages, like Chinese, Japanese, German, French, Russian, Spanish, Hindi,.. Then there is a ton of proprietary and sometimes secret information held by companies and crucial for their functioning.