Sorry for not fulfilling your expectations, but we are not able to constantly monitor and answer forum questions. Even if we try at least to sample it time to time the truth is we answer forum questions rather incidentally. The reasonable step is to write email to us directly if you are not able to get answer in forum in some meaningful time.
I'm afraid my answer to your question isn't possibly going to completely satisfy you anyway. Unfortunately, we were forced (by external forces we weren't able to influence) to massively speed up the release of DMCP system interface, therefore it isn't in the state we would like it and the documentation is missing. We wasted so much effort for this abrupt change of our plans that it isn't even clear how soon even slight SDK interface description could be available. That is also reason for NOMAS state of the SDK.
So, we put it as kind of bonus for people able to figure out how that could be used. And supported that effort by providing more elaborated example code https://github.com/swissmicros/SDKdemo
(but not so tangled as DM42PGM itself). This SDKdemo could be actually taken as the starting point for SDK use. The basic structure of code for power management, LCD, keyboard and menu usage could be seen there and reused in development.
is rather useful just for build environment test and not as a base for actual development.
Despite the NOMAS state of the SDK our general attitude is to answer emails related to the SDK and help as long as our other load allows.
Now, after explanation of the background the answer to your initial questions is obvious ... look at more examples of usage of those functions and the functionality should become clear, look at declaration of variables and it should become clear what it means (like t24 is pointer to disp_stat_t). And answer to "What user should do in order to write string in to position of row=5, column=8 of LCD?" - you could use fixed font and calculate appropriate display coordinates so it reflects your idea of row/col on LCD.