Cognominating is a fancy word that simply means to give someone a nickname or a surname. There are many other words that can be used to refer to this same act. For example, you might say that you bestowed a moniker upon someone, or that you dubbed them with a specific name. You could also describe the act of giving someone a nickname as christening, labeling, or characterizing. Other synonyms for cognominating might include identifying, calling, nominating, titling, and specifying. Whatever word you use to describe this act, the important thing is that it represents a form of endearment and recognition for the person being named.