Only the part that is specific to the company's own product or process. Knowledge that any well-trained controls technician holds does not qualify; knowledge of the employer's proprietary configuration library or methods, held by few people and needed in the United States, can.
Draw the line between the trade and the company
The statute defines specialized knowledge as special knowledge of the petitioning company's product, service, research, equipment, techniques, management or other interests and its application in international markets, or an advanced level of knowledge of the company's processes and procedures. Comparisons with other workers can be useful evidence, but there is no U.S.-labour-market test and the knowledge need not be narrowly held inside the company. Hypothetical example: a Boischatel building-automation firm's commissioning specialist knows the ordinary controls trade, which does not count, and also knows the firm's own configuration library, its naming standards, its fault-diagnosis routines and its history of site-specific adaptations, which can.
The petition should show how that knowledge is special or advanced, why the U.S. entity needs it for a particular project or expansion, and why transferring it is the point of the move. The year abroad, the corporate relationship and the doing-business requirement apply exactly as they do for L-1A.
Five years is the ceiling.