Hi Pankaj
IMO such monitoring feature is not available, you can get to know the count of messages in the Topic/Queue by searching the Tables with Destination ID in NWA-> Open SQL Browser . Can you try setting up Hermes JMS connection with PI topic/queue as mentioned in below blog.
Thesis on enabling publish/subscribe model in SAP PI 7.1(JMS)
HermesJMS is an extensible console (http://www.hermesjms.com/confluence/display/HJMS/Python) that helps you interact with JMS providers making it easy to browse or search queues and topics, copy messages around and delete them. It fully integrates with JNDI letting you discover administered objects stored, create JMS sessions from the connection factories and use any destinations found. Many providers include a plugin that uses the native API to do non-JMS things like getting queue depths (and other statistics) or finding queue and topic names
Regards
Srinivas