Here is a very simple question that seems to be taken for granted in
most academic papers. How do I calculate the number of Rount Trips for
a client server transaction over a network?

Or more specifically, Given a HTTP transaction like downloading a
page(TCP is the transport layer protocol here) how do I know how many
round trips my particular transaction took. I am not looking for the
Round Trip Time(RTT)  which can be given by using tools like
ping,tracert, etc. but rather the number of such RTTs taken to finish
a transaction.

Thank you in advance

Take the number of trips inherent in the protocol (e.g. HTTP
authentication involves extra traffic).

Allow for fragmentation above the MTU.
Guess whether Nagle timing gets you any variation on that.

Test your predictions on adequately representative cases and there you are.