There are numerous literary devices present in the anonymously written "Lord Randal." For clarification, some translations spell the poem's name "Lord Randall."
First, anaphora is present in the poem. Anaphora is the repetition of the first word/s in subsequent lines of a poem. Lines 1-2 repeat "Oh" and "O." Although different words, the sounds are the same. Lines 5-6 repeat the words "where." Lines 9,10, 13, and 14 all repeat the word "what." Lines 17-19 all repeat the word "O."
One could argue a couple different ideas regarding the use of questions in the poem. More simplistically, one could identify the use of the questions as rhetorical questions. Rhetorical questions are not meant to be answered. They are meant to make a point or ensure some type of dramatic effect.
One could also identify the use of questions as ubi sunt. While the typical use of ubi sunt is to question where those who have come before "us" have gone, here it is used to question the fate of the speaker's son.
In regards to sound, the poem contains alliteration. Alliteration is the repetition of a sound at the beginning of adjacent words. For example, line three contains two different alliterative sounds: "wild" and "wood" share the "w" sound and "mother" and "make" share the "m" sound.