In the user variables list the standard variable $$cpQuizInfoStudentName$$ is missing. Why??
You are correct, that is a user variable. It is created automatically with each new project, along with cpQuizInfoStudentID. If no one has deleted that variable, you should be able to see it. You don't see it in the Variables dialog box? What happens when you start a new project, do you get that variable?
How can i get thus variable back in the list so i can use it
Can you check with a new project? That variable may not have a value, because it only gets it when the course is deployed on a LMS and that LMS allows to get data from the learner account.
All my other projects have this variable. Also when i start a new project the variable is in the list. Only in this project i missing it.
It means that you or someone else deleted it. Did you try to recreate, since it is a user variable? For which purpose do you need it, is it to retrieve its value from a LMS?
The solution is so simple.
Make a new variable with the same name. It works in my lms.
Sometimes the most obvious solution seems too simple, indeed. You have full control over user variables.