First of all, a subreport is also a report, this means that everything you do with a report you can do with a subreport. A subreport is a resource of the main report, this means that on the server, it cannot be treated as a report but as a resource, not to be confused with what was mentioned at the beginning, subreports are also reports but when they are treated individually, when they are embedded within a report so they become content resources. JasperReports Server does not work with jasper files but with jrxml, when the path is absolute like the one mentioned in your example, these are uploaded as jasper (from Jaspersoft Studio), it is not ideal, when the path is relative and points to the server it is mandatory to use the jrxml. You can see the subreports as resources of a report in JasperReports Server by selecting the report that contains the subreport and clicking edit, then select controls and resources and all the resources used by the report, including the subreports, will appear there. You can upload the subreports to the server individually, but they should be as jrxml, this is ideal, since you can then point them to one or several reports, this is useful to avoid uploading the same resource to the server. I hope I've helped. Saludos :D
