The company's own written procedures and work instructions, records showing which of them the employee authored or revised, training materials they developed, and correspondence showing decisions escalated to them. A supervisor's comparison of this employee's knowledge with what a competent industry hire would bring is also useful.
The evidence is boring on purpose
Files that persuade in this area tend to look mundane: version-controlled procedure documents with an author's name on them, a training register showing who taught whom, a log of investigations that were referred upward, an email chain where a difficult judgement call was made. Awards, testimonials and organizational charts add little because they speak to standing rather than knowledge. It helps to assemble the material before drafting the petition, so that the narrative describes what the documents actually show instead of the documents being retrofitted to a narrative. Where a company has poor internal documentation, that is itself a finding worth knowing early. A licensed U.S. immigration attorney should decide what belongs in the filing and how it is presented.
Build the record around artifacts created before the petition: internal manuals, access histories, training materials, change logs, and messages assigning unusual problems. Then ask a manager to explain what those artifacts reveal, rather than asking for praise. The file must also establish qualifying foreign employment with the related organization for twelve continuous months in the relevant three-year period; L-1B has a five-year aggregate limit. Hypothetical example: A medical-device packaging firm relies on a technician's sterile-line calibration method. A dated validation report and training roster may answer the specialized-knowledge issue better than a long reference letter.