How to spy on what messages are walking between two applications?

Question

QNX

In QNX, the application server is spinning. Its function is to issue parameters on request (temperature, pressure, etc.). There is a client application on the same QNX that receives data from a server application. The task is to understand how these 2 applications interact with each other (what requests and in what channel the client sends requests to the server and what they will answer) in order to write your own application that will ask the server for parameters + process them.
There is such a manual on Message passing, but what if there are some other methods / utilities for software reverse engineering on QNX.
QNX version 4.25