This sentence is an example of a sentence with a predicate nominative. In this instance, the noun "example" is the predicate nominative, as it is the noun that identifies itself with the subject "this sentence." Crucially, it also follows a linking verb which serves to equate both subject and predicate nominative.
Another example of a sentence with a predicate nominative is "A baby’s first words are important developmental milestones." Here, the predicate nominative "milestones" serves to qualify the subject "words" and links to it with the verb "are." In the sentence "Congress is a legislative body," the word "body" is the predicate nominative, as it refers directly back to "Congress," linked by the verb "is." Yet another example is "Stanley Kubrick was a film director"; here, "director" is the predicate nominative, describing the subject "Stanley Kubrick."
A predicate nominative complements - which is to say that it identifies, qualifies, or helps clarify - the subject of a sentence or phrase contained within it. It is a word or group of words that has to follow a linking verb or verb phrase that is usually some form of the verb "to be," such as "is," "are," "was," "has been" and "can be." A predicate nominative is always a noun or pronoun that provides information that categorizes the subject in some way.