With the organization's own records: protocol authorship and revision history, validation and deviation reports, training materials, and a signed statement quantifying how many employees hold comparable knowledge and how long a replacement would take to train.
The records already exist in the quality system
Food and pharmaceutical producers usually have better documentation for this than they realize, because regulated quality systems record who wrote and approved what. Protocol documents carry authors, dates and revision histories. Validation reports show who designed and signed off the parameters. Deviation and corrective action records show who investigated problems and what was concluded. Training matrices show who is qualified for what and who delivers the training. Extracting those and presenting them in a short bundle, with a covering statement from the quality or operations director explaining what the documents show, makes an argument that no amount of descriptive prose can. Documents in another language need certified English translations, and any redaction for commercial reasons should be explained.
Hypothetical example: Asha works for a Canadian medical-imaging software company and has unique knowledge of its data-conversion tool. Her first review should connect each claim to a contemporaneous record: version histories, client implementation logs, internal training materials, and supervisor statements that identify her role. A corporate chart and payroll records address different issues and should not be substituted for technical evidence. She should build a concise exhibit index showing what each record proves. Petitions often fail when broad letters repeat that knowledge is special but the underlying documents show only ordinary familiarity with commercially available software.