Identify the underlined clause in the sentence "I know the place where he was born." 

The question is asking you to identify the underlined clause in the sentence "I know the place where he was born." The underlined clause is "where he was born." This clause modifies the noun "place." An adjective clause modifies a noun or pronoun and usually begins with a relative pronoun like "who," "that," or "which." In this case, "where" is a relative pronoun, making it an adjective clause. Therefore, the correct answer is "Adjective clause."