Hi Steven,
A simple method to verify this is to do it on a hop-by-hop basis, first from source to destination and then for the return traffic as well. On your routers (and most switches), you can use a policy map with no actions just to use it as a counter:
SW1(config)#class-map EF
SW1(config-cmap)#match dscp ef
SW1(config)#policy-map COUNTER
SW1(config-pmap)#class EF
SW1(config)#interface GigabitEthernet 0/1
SW1(config-if)#service-policy input COUNTER
And monitor:
SW1#show policy-map interface GigabitEthernet 0/1
GigabitEthernet0/1
Service-policy input: COUNTER
Class-map: EF (match-all)
0 packets, 0 bytes
5 minute offered rate 0000 bps
Match: dscp ef (46)
Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0000 bps, drop rate 0000 bps
Match: any
That is a simple way to test it. You can also use the show mls qos command on the 29xx/35xx switches to see incoming marked traffic:
SW1#show mls qos interface FastEthernet 0/1 statistics
FastEthernet0/1 (All statistics are in packets)
dscp: incoming
-------------------------------
0 - 4 : 0 0 0 0 0
5 - 9 : 0 0 0 0 0
10 - 14 : 0 0 0 0 0
15 - 19 : 0 0 0 0 0
20 - 24 : 0 0 0 0 0
25 - 29 : 0 0 0 0 0
30 - 34 : 0 0 0 0 0
35 - 39 : 0 0 0 0 0
40 - 44 : 0 0 0 0 0
45 - 49 : 0 0 0 0 0
50 - 54 : 0 0 0 0 0
55 - 59 : 0 0 0 0 0
60 - 64 : 0 0 0 0
Of course there are also some network monitoring tools that do this on a larger scale, checking your policy-maps or netflow.