Translation:Cé a íocann?
This may have been covered elsewhere, but what's the function of a here? I realise it's the same a that occurs with atá... is it just for question formation?
With cé and other question words there's an implied copula, thus you need the relative clause, marked with a.
A more literally translation of this is "Who is it that pays?"
ah interesting, thanks for this. Do you happen to know of a page that explains the analysis/questions in irish in more detail?