A woman to her friend: "My son finally got his dreamed work. Now, he works with promoting and generating new business at restaurants and he is a specialist in knowing the potential customer and cuisine." "Is he a cook?", - she asked. "No, he is a manager". What manager does she mean?

The woman means a business manager or a marketing manager. This is because her son's work involves promoting and generating new business, and he specializes in understanding potential customers and cuisine, which are typical responsibilities of a manager in the hospitality or marketing sector, rather than a cook.