Since you are unclear exactly what speech you are asking about, I can only assume that Romeo's long speech about Juliet that you are asking about is the most famous of them which is in Act 2, scene 2. This speech begins at the very start of the scene when Romeo is hiding in Juliet's yard. The first rhetorical device that Romeo uses is personification in the very first line when he says,"
"He jests at scars that never felt a wound." (A.2, s.2, l.1)
Here, the personification is that a scar can actually feel something. This is also an example of imagery. The next example appears in line 3 when Romeo says,
"...Juliet is the sun!" (A.2, s.2, line 3)
This is an example of a metaphor comparing Juliet to the sun.The next four lines contain a continuous example of personification. Romeo is giving life to the sun and the moon while he continues his comparison to Juliet when he says,
"Arise, fair sun, and kill the envious moon,
Who is already sick and pale with grief
That thou her maid art far more fair than she.
Be not her maid, since she is envious." (A.2, s.2, lines 4- 7)
Romeo also uses alliteration in a few lines. An example is from line 17 when he states,
"To twinkle in their spheres till they return." (A.2, s.2, line 17)