I have to train a group of people which's only knows C language and no electric/electronic background
I pity you.

The objective of the training is to make them able to do AT89C55WD programming in C language towards their application

can anyone help me on what n how to train them and what is the silibus

In either case you need use the first 3 chapters of the '51 "bible" SEE LINKS <---- for address. Regardless of C you need ch2 for the SFR definitions.
I also believe that there is some text at the Keil website, whether from there or elsewhere you need find some XDATA/IDATA/EDATA/BDATA/DATA/CODE/SFR text.

Erik

Erik