Where exactly is the rising action in the story "Thank You, Ma'm" by Langston Hughes?

That depends--if you think that the climax is where Luella drags the boy home instead of calling the police on him, then the rising action would be all of the events leading up to that time. For example, Luella walks home from work, the boy tries to snatch her pocketbook, they fall down, she snatches him up and drags him home.

The climax is the part of the story that has the most intense action (internal or external) and this story has several plot points that you can interpret and support as being the climax.

The rising action is everything that comes before that point.

The link below will help you sort out the "pieces" of the plot.