It is a common use case to report on request items and the related variable values. This is not easily accomplished using the Service Now Report Builder. There are two options available, documented here.
The first way is using the native report builder but you are limited in the types of reports you can create.
Note: List, Box, Trendbox, and Pivot reports cannot use service catalog variables as a primary or secondary Group by. Single Score, Calendar, Control, and Map reports do not support Group by on any fields. List reports can use service catalog variables as columns.
The second comes from a Community post, using a database view to create your report.