Questions on Decision Making have been asked in XAT for quite a few years.
However, their importance has gone up drastically since 2012. Before that, you could expect 8 to 10 questions on Decision Making in the Analytical Reasoning section. In 2012, Decision Making became a section of its own and if you were to look at it purely from a scoring perspective – it make the most important topic for a student who is planning to write the XAT.
These kinds of questions require a logical approach and a clear understanding of the situation. It often requires going through large amounts of text and then logically interpreting the information presented. To put it in conventional terms, it is a combination of Reading Comprehension and Logical Reasoning and traditionally students who are good in these two areas tend to do well in the Decision Making section as well.
A good way to prepare for Decision Making would be to look at previous year papers. You can have a look at questions from XAT 2008 to XAT 2020 which would give you approximately 300+ questions to practice. These 300+ questions will not only tell you your current level of understanding of the topic but if you analyze them properly, it can make a difference to you final score.