What is the ruling on taking a commission from another engineering firm that was nominated to complete a work that is not within the specialization of the office where I work, and must this commission be given to the owner of the office?

There is no blame upon the questioner for taking a commission from the client, as long as the mechanical works are not within the scope of his office, and the nomination requested by the client is not part of his work for which he receives a salary. It is not affected by the fact that he met the client through his work in the office.