You can get some idea by looking at where the packages are going - but in todays ipv4 space, most p2p packages have to transit trough some public IP addresses. That means that, unless you are able to decrypt the traffic, it will be difficult to know if someone is listening in on the conversation. Also, just by looking at the packages, you will not have any means to detect back-doors, unless they are accessed while you are looking. Back-doors potentially requested by intelligence agencies for snooping on high value targets are likely to go undetected.