I work in a service provider environ. We are providing qinq to customer in l2VPN service. How can I do traffic marking and classification on s-vlan.
In general, any QoS features (DSCP values etc) that are applied at Layer 3 are maintained when traversing any Layer 2 configurations such as L2VPNs and QinQ. For layer 2 QoS features (CoS values) that are applied in the VLAN tag, as long as the VLAN tag is intact, the QoS markings will remain constant.
QoS markings can be applied at various locations. For traffic that traverses pseudowires, you can take a look at this Cisco documentation for more information about QoS:
Can you share with us a little more of what it is that you would like to achieve? This way we can more readily make suggestions that will help you more effectively.
I hope this has been helpful!