What punctuation mark should be placed at the end of the sentence?
Have you finished reading the book

Correct option is B

Correct punctuation mark: (b) Mark of interrogation (?)
Why (in detail):
• The sentence is a direct question (it asks something).
• Direct questions end with a question mark (?).
Grammatical Rule (English):
• Interrogative sentences end with (?).
व्याकरणिक नियम (Hindi):
• प्रश्नवाचक वाक्य के अंत में प्रश्नवाचक चिन्ह (?) लगाया जाता है।
Hence, option (b) is the correct answer.