Only the part that is the company's own process qualifies. General trail-building skill, however advanced, is not specialized knowledge; the firm's documented build specification and the builder's advanced command of it can be.
Draw the line between the trade and the company's method
The distinction that decides this case is between what any experienced trail builder knows and what only someone trained inside this firm knows. Excavator operation, rock armouring, bench cutting and drainage are the trade. The firm's specification, which dictates how designs are translated into machine passes, how sections are inspected and how crews record deviations, is the company process.
Specialized knowledge is claimed on the second layer, and it has to be advanced: the senior builder wrote the specification, revised it after several seasons, and is the person who certifies other crews. That is different from a builder who merely follows it. Describe the knowledge in terms a reviewer can test, with examples of decisions the specification governs and the consequences of getting them wrong, such as trail failure after spring runoff.
The affiliate's need is then plain: it has a state contract requiring the firm's standard, and nobody in Vermont has been trained to deliver it.