Doing proper OSINT research requires an excellent knowledge of open sources.
Next to the many open source resources already offered, the Repertorium or OSINT Resource Discovery Toolkit, helps in finding the right sources for the right answers. There is amongst others an extensive listing of categories of search engines, each with one or two primary examples. Each listing has direct links to the help pages to find out exactly how each search language works.
The Repertorium is the companion to our range of OSINT training programmes and workshops. Interested? Have a look at https://triangulargroup.com/en/osint.