Kilkenny to Cork

Google says there are buses, which take anywhere from 3 1/2 hours to 7 depending on when you go and how many connections you need to make. Driving looks to be as short as an hour and 40 minutes to 2 and a half hours.

Have a look at www.hittheroad.ie or www.a-b.ie for transport queries.

You can check on this site:
https://national.buseireann.ie/

Buses are very cost effective in Ireland, might not always be very fast though. They seem to route the Kilkenny to Cork buses through Waterford, which is going out of your way. Trains are also a potential option but they seem to go through Dublin, also very circuitous http://www.irishrail.ie/

I have never taken a train in Ireland. I have taken several journeys on buses, and they work great except as in many countries the legroom is very limited. Worse than a coach seat on a plane.

Renting in Kilkenny might not be a bad idea, there are a number of sights on the way or in the vicinity of Kilkenny. Jerpoint Abbey, Cahir Castle, Rock of Cashel could be visited on the way. Also Cobh is worth at least a quick stop.

I did this route many years ago, but the other way around, plus I made a stop in Cashel to see the Rock of Cashel. I recall getting the bus from Cork to Cashel was easy, but getting from Cashel to Kilkenny involved getting a bus to a train station and then the train to Kilkenny so it might work better if you were to just search for a bus that went to the nearest train station then just take the train to Cork. I'm sure some schedules have changed since I was there, but it might be worth your while to look at the journey in two parts when you search. Instead of trying to find the most direct route from Kilkenny to Cork maybe try searching for a bus to Cashel, then a bus to Cork. The Rock of Cashel is definitely worth a look and I remember it was a short walk from the bus stop.