I want to retrieve the Scheduled Time Off details for specific Agent based on Agent User ID and Date Range without providing any other details like business units or management units, etc. Which WFM API would will provide the details/filters.
You noted 'scheduled' if you really want to know time off requests that are scheduled on published schedules, then that will be very difficult. You would have to search for agents schedules and examine for scheduled time off requests. If instead you want to know those that have been approved, then my answer above is sufficient.