My friend is a british citizen and engaged to a hongkong citizen who resides in hongkong , they would like to marry in dublin as her son wishes to attend her wedding, her son is an irish citizen , what procedure would they have to follow

This is a link to the general laws for marrying in the Republic of Ireland: The General Register Office - Getting Married

It might be best if she or her son contacts the Registrars office for the District she wants to be married in to find out exactly what is needed so there are no misunderstandings.

Congratulations to her and her intended and may it turn out to be a simpler process than it appears.