how Does Google Know Everything?

Google does not know everything. Google has bots/crawlers which basically crawl the internet and database to collect the information. Database which is not organised in correct form so they match the search query and filter the data from trillions of website and the website which best suited as prospective to Search Engine Optimisation (SEO) it’s bots show them on Search Engine Result page.
Google has its own data center where they keep on storing all the information shared and submit by the webmasters.