Here's an example from "The Road Not Taken":
"Two roads diverged in a yellow wood,
And sorry I could not travel both
And be one traveler, long I stood
And looked down one as far as I could
To where it bent in the undergrowth;"
* Notice the repetition of the short "u" sound in "wood, could," and "undergrowth".
Other examples:
* "Stopping by Woods on a Snowy Evening":
* "The woods are lovely, dark and deep" (repetition of the long "oo" sound in "lovely," "dark," and "deep")
* "Mending Wall":
* "Something there is that doesn't love a wall" (repetition of the short "a" sound in "that," "doesn't," and "a")
It's worth noting: Frost often uses assonance subtly, creating a sense of rhythm and flow in his poetry without making it overly obvious. To find examples, you can look for repeated vowel sounds within a line or across multiple lines of his poems.