"Do you help or does he help?"
Translation:An gcabhraíonn sibh nó an gcabhraíonn sé?
cabhair is a noun meaning "assistance"
cabhraíonn is a verb meaning "help". an gcabhraíonn tú = "do you help" This is the "correct" answer.
cabhraír is an alternative to cabhraíonn tú (along the lines of cabhraím / cabhraíonn mé). It's the usual form in Munster, but considered old-fashioned elsewhere - although you do hear it outside Munster. I think this answer should be accepted as an alternative, but Duolingo might not - it could cause confusion when no mention is made of it in the notes!
This is an example of eclipsis, a grammar rule and initial mutation you would have been introduced to early in the tree (In the Eclipsis skill, right next to lenition and represented by a cog). In the present tense verbs are eclipsed (if possible) after the interrogative particle"an"