Final answer:
Sam's cognitive ability is best described as convergent thinking.
Step-by-step explanation:
Sam's cognitive ability, as described in the question, is best characterized as convergent thinking. Convergent thinking refers to the ability to narrow down options and arrive at a single correct answer or solution to a problem. In this case, Sam only considers using a table knife for cutting food and does not think of it as a tool to pry a stuck window loose. This demonstrates a lack of divergent thinking, which involves generating multiple solutions to a problem.