Who is the modern man in "The Man with the Hoe"?
I am assuming that you are asking about Edwin Markham's poem, which is based on a painting with the same title. The man in the poem is clearly meant to be a man for all time, representing ancient workers, workers at the time of the publication of the poem, which was in the late 1890s, and workers to this day.
In the modern world, there are people all over the world, men and women, who continue to carry "the burden of the world" (line 4), who are so exhausted by their labor they cannot even feel "rapture or despair" (line 5), in other words, great joy or sadness. These are people who are "Plundered, profaned, and disinherited" (line 30), so taken advantage of by the greedy that they have no lives, no spirit, and no minds, little more than animals because of how they are treated.
In spite of the fact that in some countries, there are some protections for workers, due to enlightened management, legislation, or union efforts, the plight of the working man and woman persists. There are countries where working people make a few dollars a day and are subject to dreadful and dangerous working conditions. They have been stripped of their humanity, too exhausted to go home at the end of the day and enjoy anything life might have to offer. Even in the United States, many people have dangerous and dirty jobs that afford them not even a living wage. And even for those who make a living wage, for example, coal miners, the weight of the world, which is literally upon them, bows them down. Migrant workers are a group of people who endure backbreaking work, as well, and it is likely one can find, right now, a man with a hoe who is the very kind of person Markham is speaking of. The fact that we are living in a post-industrial age has not made Markham's man with a hoe disappear. Lamentably, he is still with us.