This is a phrase which varies a lot according to dialect. In my dialect (Ulster Irish) we say "Goidé mar atá tú?" (Cad é mar atá tú?). In Connacht Irish you are more likely to hear: "Cén chaoi a bhfuil tú?"; and in Munster Irish: "Conas a tánn tú?" or "Conas taoi?".

There is also the very common "Conas (a)tá tú?".