Hello David
It depends on what you want to achieve. If you’re using a policy map to mark telnet messages, then there will be little or no difference whether you mark them incoming on G2 or outgoing on G1. The purpose is to have them marked for transmission throughout the whole network. The direction (inbound or outbound) mainly affects the order of operations for other features like routing, NAT, etc, but for classification, it doesn’t really matter. The only time it would matter is if you have configured R1 to process these telnet packets with a particular QoS priority, thus, when the packets are being processed within R1, if you apply it in an inbound direction on G2, those priorities would be applied for the packets as they egress the device.
The marking of CS6 is likely due to the default behavior of Telnet. The Telnet responses (from the Telnet server to the client) are typically marked as CS6, which is the default ToS value for network control traffic. This is because Telnet replies are considered as network control traffic, thus they are marked with a higher priority value (CS6) than regular traffic. The reasoning behind this is the same as that seen on OSPF messages.
I hope this has been helpful!
Laz