saved Reports in content store

[Joker]

Can you please tell me the following two questions- 
1.When a report Specification is saved in a content store.What is its Extension? 
2.Package extension in Content Store? 

[Michael75]

1. N/A
2. N/A

The Content Store is a database (Oracle, DB2...  whatever you use at your site) which contains metadata (so the question about file extensions is not relevant).

Reports and packages exist as entries in different tables of this DB; they too are metadata. IBM Cognos intentionally does not document these tables, because their layout and content are subject to change from one version to the next.

Nevertheless, by searching on this site, and elsewhere on the Internet, you will be able to get at least a partial understanding - maybe sufficient for your purposes? - of what can be found where.