In order to use the reports option provided in Jira Service Desk you will need to give the user an agent licence. A user with a project license can run reports but they are limited to the project reports and they will not be able to create or view service desk reports.
It's kind of tragedy that you can't use Jira Standard Reports provided by Jira Core in Jira Service Desk/Service Management, beside the fact that the link for the standard reports is still working for Service Desk projects... They just killed the button. Makes no sense.