Material does not mean "would move the market." It means there is a substantial likelihood that a reasonable shareholder would consider it important" in making an investment decision". https://www.sec.gov/rules/2000/08/selective-disclosure-and-i...

You can visit their offices and talk to the employees.

If an employee tells you something that is nonpublic information, and you act on it, that would likely be considering insider trading by the SEC. There is a fair amount of case law supporting this point. Indeed, the fact that you acted on the employee's information is generally sufficient proof that the information was material; and this is in fact the most common insider trading scenario.

You can also derive material information for instance through freedom of information requests. Is a business being investigated by the SEC?

If the target of the SEC is not aware of the investigation, the SEC will not disclose that information in response to a FOIA request. On the flipside, if a company is being investigated by the SEC, and knows it, that is material information that must be disclosed to the market.

If you watch the company parking lot and notice that the finance department and CFO stay at work until 11pm in the week leading up to their earnings report you are free to short the stock based on this info.

Such behavior would provide no useful information about the state of a company's financials. In the week leading up to earnings reports, the CFO and finance departments generally stay late making sure the financials are in proper shape, whether or not those financials are good or bad. This is standard practice at all publicly traded companies with proper controls, because there is a very short window of time between the end of the financial period and the time it must be reported for regulatory purposes.