In all of the episodes of Star Trek: Voyager that I've seen, I've never heard anyone call Commander Chakotay by any other name. This includes formal and informal settings. Does he have an official first/last name, or is Chakotay his full name like it is for Data?
Chakotay is a mononym
Robert Beltran (the actor who portrays Chakotay on Star Trek Voyager) was asked this question in a fan interview session. Although his reply seems mischievous, his lack of a genuine response strongly implies that his character only has one name.
Interviewer : What is Chakotay's first name in the Voyager series?
Beltran : Fred.
The idea of him having a singular name is borne out by his gravestone in VOY: Endgame, Part I,
his personnel file on the Valjean in VOY: Caretaker
and his entry on the official StarTrek.com website