Which of the following amendments focused specifically on citizenship rights?

The 14th Amendment is specifically focused on citizenship rights, as it was enacted in 1868 to address issues related to former slaves following the Civil War. One of its key components is the Citizenship Clause, which grants citizenship to all individuals born or naturalized in the United States. This amendment also provides for equal protection under the law and due process, which are crucial elements in protecting the legal rights of citizens.

In contrast, the 13th Amendment abolished slavery and involuntary servitude, while the 15th Amendment prohibits the denial of voting rights based on race, color, or previous condition of servitude. The 16th Amendment establishes the federal income tax but does not pertain to citizenship rights at all. Therefore, the focus of the 14th Amendment on defining and protecting citizenship makes it the correct answer in this context.