In the poem "Success is Counted Sweetest" by Emily Dickinson, what poetic devices can be found in it?

There are several techniques in the poem.  The first is rhyming The words that rhyme in her poem are "succeed/need", and "ear/clear".  She also uses imagery in the last stanza (imagery is using the 5 senses to describe something).  She describes, "On whose forbidden ear/the distant strains of triumph/Break, agonized and clear."  She is describing the sounds of triumph very descriptively, which is imagery.  She also describes the army as a "purple Host", an image that fits with imagery.

Then, for figurative language techniques, there is a metaphor.  She compares people who appreciate success the most to someone who appreciates nectar because they are starving.  She says, "To comprehend a nectar/requires sorest need."  This enhances the point that she is making, that success often is counted the sweetest to those who have fought and struggled for it, and never tasted it.

I hope that helps!