I know that the source code of linux kernel is licensed under GNU GPL V2.
Is there a way to view the change done to a module by a corporate company(say Cisco,Oracle)?
Since the module must be disclosed once they change the code to fit their binary blob.
An individual or organization can put their code under any license they like, but unless it is GPLv2 or a compatible license it a) will not/cannot be included in the mainline kernel which can slow down adoption of the code, or b) cause legal issues for its users.