How to know key of list instance?

I have a list of records. And i have subscribed at top level.

Now application has modified the xth record leafs having key value as 10.
This trigger the subscription notification to subscribed application.
Is there any way on receipt of notification to know which record is updated.
means how subscribed application will know record having key value 10 is changed.

Can application fetch the list of modified keys ? I dont want to use cdb_diff_iterate as it will run through all modified keypath. my requirement to get modified key and if required read all key path of that key

You can use cdb_diff_iter() where your iter() function return ITER_CONTINUE to ignore the children.
See also cdb_get_modifications(), cdb_get_modifications_iter() in the confd_lib_cdb(3) man page.