Question

How do readers know that hughes is alluding to walt whitman’s poem, “i hear america singing”?

Answer 1

Well, there are some simple but very deep lines written by Hughes which pose as an allusion to the Whitman's poem, and the way readers can recognize it during acquaintance with these authors is being hidden inthe very first line of the poem (“I, too, sing America”) which is commonly known as a direct response to Whitman’s “I Hear America Singing.”
I am pretty sure it will help you!