To obtain the  Student Enrollment ID number (Register ID) we had to pull it from a list.
Each Year a User is Enrolled in School there is a Enrollment Row created for the Student. In this record lives a Registration ID
Create a list by navigating to any Dashboard and clicking
  1. Lists
  2. View All
  3. List Templates
  4. Constituent Information
  5. Registered Students (Current Year and/or Next Year)
  6. Click View/Copy
  7. Add the Display Field by clicking the + icon, User Register.Register Id
  8. Click Filters
  9. Change Filter to User Register.School Year is any of 2015-2016 (select the year(s) you are looking to display)
  10. Add another filter by clicking the + button
  11. Select User Base.User ID is equal to the User you are looking for (if you do not need just one specific user you can leave this filter out)