This is how
you should do.
[1] In the InfoMessageBroker-v2016.xsd, add the import (add path to the schemaLocation, if necessary) and modify the root. This is the first two lines followed by the definition of the element EventMessage as written in your original xsd.
[2] Then inside the same schema, change the type to the EventBody line
[3] Furthermore, to reinforced validation, you should really change the processContents attribute from skip to lax, or preferrably to strict, since you take the trouble to construct the schema for the namespace pbn surely for a purpose, and to import it.
[3.1] If you keep the processContents skip, you don't even need to import the PDNotification-20180914.xsd into InfoMessageBroker-v2016.xsd and the validation of the message will go through without any problem at that level already.
That's all you need to do.
ps: This should also be the answer to your another thread
https://coderanch.com/t/702056/languages/Suggestion-tag-xsd
which is practically the same as this one.