Unfortunately, the Prolific guide only includes a vague answer to which demographic items I will have access to when running a study without needing to ask for them. So what are they exactly?
Dear Kyr
Welcome to the forum 
You will have access to the following in the demographic data download plus the participants answers to the screeners that you used.
Session id
Participant id
Submission status
Started date-time (in GMT)
Completed date-time (in GMT)
Time taken
Age
Sex
First language
Current country of residence
Nationality
Country of birth
Student status
Employment status
Number of approvals
Number of rejections
Approval rate (‘Prolific score’)
Reviewed at date-time (in GMT)
Completion code (‘entered code’)