Is there anywhere in Dublin I can go to discuss Islam ?

Here is probably best if you want to speak to someone in person. I'm sure if you ask anyone there they'd point you in the right direction, there's always people about.

The above is a predominantly Sunni center, so if you'd like to get the Shia side too you can go here. Best to go during prayer times to this one though as there's not many people about at other times.

Just walk into a mosque if there is one near you. Usually the lads love a good debate :-) Seriously though, you will find people there who will answer your questions.