Dear Mohamed-Mourad Lafifi , thank you for your answer. The references provide information about the methods that work based on the reference-point and sampling reference-points to be used with performance indicators in the evaluation stage. However, there is no information about how does the DM determine the reference points, for a particular problem, to be used with reference point-based (or preference-based) optimization algorithms.
There are no clear guidelines on how a DM determine reference point. In most of the cases it comes from past experience, problem knowledge and expert opinion. The way to select reference points depends upon type of problem too. For e.g. in case of some multi-objective design optimization, the reference points can be individual optima of each objective function.