Unable to determine quantity of times or who has called the REST API.
To determine how many times the REST API has been called, a query for the count of records based on job_name or job_class_name should be submitted.
This information is stored in QRTZ_JOB_DETAILS. Each time a REST API is called, a record is inserted into this table.
In order to determine who submitted the REST API, there is a column called created_by in the gtrep_job_information table.
If needed, a query could be written to extract that data.