Sentient: Conscious, experiencing sensation or feeling, having faculties of sensation, endowed with feeling and unstructured consciousness. My dog is Sentient. My Cat is arguably so. I certainly am.
Sapient: Having great wisdom and discernment, wise, sage, acutely discerning, insightful, observant, thoughtful. This suggests to me to require something more than the inscrutable Wisdom of Cats or the highly sensitive judgement of character possessed by Dogs. I think this requires intelligence, which may in turn require communication, in order for concepts like language, discernment, and structured thought to really apply.
Sophont: Intelligent being (including aliens)
Person:
1. A living human. Often used in combination: chairperson; spokesperson; salesperson.
2. An individual of specified character: a person of importance.
3. The composite of characteristics that make up an individual personality; the self.
4. The living body of a human: searched the prisoner's person.
5. Physique and general appearance.
6. Law. A human or organization with legal rights and duties.
7. A living, self-conscious being, as distinct from an animal or a thing; a moral agent; a human being; a man, woman, or child.
With thanks to dictionary.com
Citizen versus Person: Any being that is self-conscious (Conscious of the meaning of self and its own selfness) is a Person, if you are willing to stretch beyond the humanocentric definitions of personhood. A Citizen is someone belonging to a polity of some sort, generally by birth, sometimes admitted to citizenship by other means, and that citizenship entails responsibilities, duties and legal limitations and confers (in some cases) protections and rights.
