Hi Subhojit,
If you want to show DocumentIdentifier objects for a speficic user on a page I would recommend applying Entity Access on your DocumentIdentifier entity. This is a more secure way to ensure users will only see the objects they are granted to.
Your Entity Access would look something like this [GlobalTracker.DocumentIdentifier_UserCategoryMapping/GlobalTracker.UserCategoryMapping/GlobalTracker.UserCategoryMapping_User = [%CurrentUser%]]
Once you have set your entity access correctly, you don't need any Xpaths or Data Source Microflow on your datagrid.
Hope this helps!