With the enterprise's own employment records: payroll registers, employment tax filings, job descriptions and dates of hire, showing at least ten full-time positions filled by qualifying U.S. workers within the required period.
Payroll is the proof
Hypothetical example: a Hampton investor plans to run the business himself and assumes an organization chart will demonstrate the jobs. It will not. The second-stage filing turns on records showing that real people held real full-time positions: payroll registers across the period, employment tax filings, offer letters and dates of hire, and documentation of each role's hours. Positions must be full-time as defined for this purpose, and certain people are excluded from counting as qualifying employees, so the definitions should be read before the hiring plan is written rather than afterwards. Two habits help: keep the employment records in a form that can be exported cleanly, and review headcount against the plan every quarter, so a shortfall is visible while there is still time to correct it.
The trail is the purchase agreement, the closing statement, the corporation's bank records showing receipt, the resolution or dividend record authorizing payment to the owners, the personal accounts receiving it, and the transfer to the project escrow.