Hello Eric,
It's great that you'll be celebrating Christmas in Dublin this year!
Was there a Church in particular where you wanted to attend the Christmas service? The
Archdiocese of Dublin website has info on mass times for each church of the region. From what I could see on the
St Patrick's Cathedral website for instance (a known church in Dublin), you would need a ticket to attend the Christmas service on the 24th, but there is a concert starting at 4pm, in case you are also interested.
I hope you'll make the most of your time in Dublin during this lovely time of the year. Here's an article about
Christmas in Ireland that may inspire you.
A bientôt,
Antoine