Hi,
the mechanism used by VTP to allow the communication of VTP pruning information is known as the VTP Join message.
Check this output, and focus on "join":
Console> (enable) show vtp statistics
VTP statistics:
summary advts received 4690
subset advts received 7
request advts received 0
summary advts transmitted 4397
subset advts transmitted 8
request advts transmitted 0
No of config revision errors 0
No of config digest errors 0
VTP pruning statistics:
Trunk Join Trasmitted Join Received Summary advts received from
non-pruning-capable device
-------- --------------- ------------- ---------------------------
1/1 0 0 0
1/2 0 0 0
Remember that network devices in VTP transparent mode do not send VTP Join messages
for more infos: "CCNP Self-Study CCNP Practical Studies: Switching"
HTH
Andrea