If you have MOH configured to stream multicast from flash on a router / voice gateway, you can use:
show ccm-manager music-on-hold

to see the current MOH sessions that are active. The output will show:

• Multicast Address
• RTP Port Number
• Packets in/out
• Call id
• Codec
• Inbound Interface (this will be the bind interface for the show ccm-manager music-on-hold bind <Interface> command)

The Call id field is good for tracking calls back through:
show voip rtp connections, etc if you need to do that.