Decoding circuit with transformer topology
I want to know which SMPS topology is used here ?


Almost certainly, it's a flyback topology. A big clue is the "opposite" dot-notation used on primary and secondary of the transformer. Dot notation polarity is very important for the correct operation of a flyback converter and the detail shown is typical of that type of design.

A 2nd clue is in the data sheet details - they give more example circuits and they all look like flyback designs to me: -