As mentioned in the beginning the GP Service supports three different tasks:
•VertiGIS_PrintTask: creates the print according to the requested parameters
•GetLayoutInfo: provides information about the template, that allows the client to show the map frames in the browser
•GetIndexInfo: calculates and delivers the map frame rectangles that cover the index line
For example in order to receive information about the print template available for VertiGIS Printing, it's possible to get the results via the Get Layout Templates Info Tasks ArcGIS Rest-Interface. The section "results" contains information e.g. about pageSize, pageUnits or customTextElements.

ArcGIS REST Interface - Get Layout Templates Info Taks