Which type of opinion should someone consult to understand why a particular Supreme Court justice disagreed with the Court's ruling on a case?

Dissenting opinion

Explanation:

A dissenting opinion is an opinion in a legal case in which a judge expresses his disagreement with the majority opinion. In these cases, the judge will also explain the reasons why he does not agree with the ruling. Dissenting opinions do not become binding precedent. Nevertheless, they can still be important pieces of persuasive information for future rulings.

This type of opinion is called a Dissenting Opinion. This happens when a judge decides against what is called the controlling opinion, which is what will become legally binding and explains his reasoning behind that decision. Reading the Dissenting Opinion by a judge is a great way to understand different sides of a question.