According to API Explorer of VMware Habor Registry 1.10.x, you may see the following API path to get the scan report:
GET /repositories/{repo_name}/tags/{tag}/scan Get the scan report
Based on this API path, you may get an empty response even if there are actual vulnerability reports with the target repository when you try to get the scan report from API Explorer or by the command line as below:
$ curl -k -u admin:passowrd -X GET "https://harbor.mydomain.com/api/repositories/testrepo%2testapp/tags/latest/scan" -H "accept: application/json"