"Cad and céard are equivalents. Cén is used before nouns. So cén fath really means what reason."
Who = cé, cé an duine (literally who is the person)
What = cé, ceard (short for cé an rud, I think), cad, cad é (also written caidé or goidé)
When = cén uair/lá/am, etc., cathain
Where = cá háit, cén áit
How = cén chaoi (literally cé an chaoi, what is the way), conas
Why = cén fáth (literally cé an fáth, what is the reason)
Yes, this course actually uses the official standard. Native or second language learners in Ireland all use the same standard. I am unaware of semi-offical or "dialect written standards". So all 3 dialects should use the exact same written, and people in school learning through Irish all use the one standard.
It's called "An Caighdeán Oifigiúil".. https://data.oireachtas.ie/ie/oireachtas/caighdeanOifigiul/2017/2017-08-03_an-caighdean-oifigiuil-2017_en.pdf
be warned its 218 pages of examples and rules, and the day you actually understand the whole lot of it, is the day youre as fluent as they come.