Justice shows up naturally. In everything that I want and need for myself, I know in some respect what you want and need for yourself. I can even make the assumption that the things that I need and want for a life that is worth living are very similar to what people in different places in the world want and need for a fulfilling life of their own. I know this because that very basic sense of justice is built into us as human beings.
This form of common justice does not require heavy thinking or in depth studies of any sort. Just start asking what kinds of things you need for the life you want to live.
Do I need healthy food and clean water? Do I need housing adequate for me and my family? Do I need health care and preventative care? Do I need an education? Do I need work that pays a living wage? Do I need communities that are safe to move about in? Do I need friends and associations that are supportive and meaningful? Do I need freedom to express myself in various ways? Do I need freedom to move about the world where I want and need to? Do I need dependable transportation? Do I need reasonable work hours and schedules?
Your list will be made up largely of the things basic to a human life that any of us would want to live–or, to put it negatively: without these things we would be unhappy living that life. We might even find living life impossible.
This basic sense of justice is natural. It is inherent in us. If I can see you, I have a basic sense of what you need, of where bounty is appropriately bestowed.