He said, “I have often told you not to waste your time.”

The correct answer is D.

He said, “I have often told you not to waste your time.”

A. He said that he had often told not to waste your time.

This is incorrect because the subject of the sentence is “he,” not “I.”

B. He said that he had often told him not to waste your time.

This is the correct answer. The subject of the sentence is “he,” and the direct object is “him.”

C. He said that he had often suggested to him not to waste his time.

This is incorrect because the word “suggested” is not the same as the word “told.”

D. He told that he had often told him not to waste his time.

This is incorrect because the word “told” is not in the correct tense.