You have 2 different options :

A - You have a 2016 valid triathlon licence from a national triathlon federation :
Add your licence and photo identification to your "bring along checklist" right away.

B - You do not have a triathlon licence :
During the on-spot race registration (in the Expo Village from Friday to Saturday morning), you will have to buy a one-day-licence from the NTB(Nederlandse Triatlon Bond) and provide the following :
* a valid photo identification
* € 28 to pay cash or buy a 1 day licence with your registration online