As part of your application for the Exam Visa to Ireland, you have to submit a detailed description of the exam you intend to sit in Ireland. The information you have to provide includes:
The name of the exam
The name of the institution or organisation holding the exam
Proof showing that you have registered for the exam
Receipt confirming that you paid exam fees
The date on which the exam will take place
Explanation why you have to sit the exam in Ireland and not in your home country
Proof that the exam is relevant for your work or study course.
If you still do not know some details such as the exact date of the exam, you can mention that in your application. Make sure to provide as much information about the exam as possible, however.