The correct answer is option 2), i.e. Can Rahul speak in French? Explanation:
Option 1) is incorrect. The comma is used when someone is directly addressed OR to separate two clauses/to separate ideas, objects, names in a sentence. Example: I will go to Goa, Mumbai and Pune.
Option 2) is the correctly punctuated sentence.
Option 3) is incorrect. The exclamation mark is used to express strong feelings like sorrow, wonder, surprise or to emphasize. Example : I have found the lost photo album!
Option 4) is incorrect. The full stop is used at the end of a sentence. Example: She is my sister.