The dominant literary device in a poem refers to the most frequently used or most prominent technique employed by the author.
Personification is a literary device that attributes human qualities to non-human objects or animals. Simile is a comparison between two things using "like" or "as". Onomatopoeia is a word that imitates the sound it represents. Alliteration is the repetition of the same initial sound in a series of words.
So, the dominant literary device in a poem can be determined by analyzing the poem for the frequency and importance of each of these techniques. For example, if there are many instances of non-human objects or animals being given human-like qualities, then the dominant literary device may be personification. Similarly, if there are many instances of comparisons using "like" or "as", then the dominant literary device may be simile.