For instance, for the incoming audio stream at the receiver, this webRTC internal function gives me the RTP timestamp!
http://www.webrtc.org/reference/webrtc-internals/voevideosync#TOC-GetPlayoutTimeStamp
You could sniff all this information using WireShark. But I am looking to access this via a javascript function request?
As you can see in the url you shared, that documentation is under "webrtc-internals" and describes how browsers should implement WebRTC inside the browser. Those low level functions are not available via Javascript.
You can find what's available (now or in the future) via Javascript here.