In a broad sense, no. An engineer, like any other human being is under no
duty to do anything, unless the law requires him to act.
However, the question is equally misleading. There is a difference between
an engineer who happens to be on the job site for a project he is doing, and
an engineer who is driving down the street and somehow recognizes a code
violation in a building under construction. The first scenario, and not the
later, probably imposes a duty to act on the professional engineer.