If you want to exposed metadata from a module to the main application AFTER the module has been loaded and initialized then a simple approach to do this is to add the metadata of the module in its Initialize method. For example, you could have a shared service in charge of storing the metadata of the modules and each module could access it and add their metadata when their are initialized.
If you want to access the metadata of a module BEFORE it has been loaded (for example, to decide which modules you want to load or not) then Prism does not provide any functionality that could help you to do this as out of the box. You can replace the default implementation of several classes related to the interactivity API of Prism to add your custom functionality (you can read more about this here,) but for this case I think it would be better implement a separate service to obtain the metadata for the modules that would then just delegate the initialization of the modules to Prism.