Answer:
The sentence "Jacob said, 'Have you read this book?'" is an example of direct speech. It is a complete sentence that consists of two parts: the reporting clause (Jacob said) and the reported clause (Have you read this book?).
In direct speech, the exact words spoken by a person are quoted and enclosed in quotation marks. In this case, the exact words spoken by Jacob are "Have you read this book?", and they are enclosed in quotation marks.
Direct speech is commonly used in writing to convey the exact words spoken by a person, and it is usually introduced with a reporting verb or phrase such as "said," "asked," or "inquired."