On grammatical class:

ge'e
attitudinal: elliptical/unspecified/non-specific emotion; no particular feeling.
ki'a
attitudinal question: confusion about something said.
xu
discursive: true-false question.
ju'opei
attitudinal: certainty question.
ki'anai
non-question: understanding of something said.
xunai
discursive: false-true question.
ko'oi
discursive: imperative/hortative