I would like to know if there is versioning feature available in Cognos 10 i.e. if a user opens a report in report studio then for other users it should be shown as locked or read only.
No there is not.
We use a third party tool that integrates right into Report Studio. It works great:
http://www.bspsoftware.com/Products/ImplementationBasedSoftware/IntegratedControlSuite/IntegratedVersionControl