Thank you for relay.
I have aksed the cisco engineer.He asks me to refer to The IPCC Reporting Guide for more information.
The Role of the Default Skill Group in Reporting
The default skill group acts as a bucket to capture information about voice calls not routed byICM/IPCC routing scripts or if a skill group is not specified in a routing script. For example, if the Agent to Agent node is used in a routing script for agent to agent dialing, data is gatheredfor the default skill group.