Do you know a way to make the process inside a call activity visible to the user when she/he click the call activity? like the expansion with the subprocesses.
And how i can know that i inserted correctly the process inside the call activity?
How call activities are resolved depends entirely on the engine you execute on. The bpmn-js instance does not have the information about the mechanism.
Therefore, if you want to create a drill-down functionality for call activities, you will have to implement the overlay, linking, and the resolution behavior as an extension.