I have tried to explain the concept and algorithm for building the Dominator Tree of a directed graph with respect to a source vertex in this article :
The algorithm was published by Robert Tarjan in his original research paper here. There are not much resources on the topic, except the original research paper , on the internet. The topic is fairly advanced and involves a lot of theory.
Kindly read and give your feedbacks !
Happy Coding :)
Edit : A link to the pdf version of the article has been added in the Blog Post. :)