We first need to make sure we know what each of the words you're finding examples of means.
Assonance is also called vowel rhyme. It is the repetition of vowel sounds in a line of poetry. More often than not, you can see this in the same word as well as several words. For example: Hear the mellow wedding bells. If you look at each of these words in that line of poetry, they each have the same e sound. That is assonance.
Alliteration is very similar to assonance, except that it is the repetition of the same letter or sound at the beginning of a word. For example: Peter Piper picked a peck of pickled peppers. In that line, the letter p and the sound of it is repeated throughout.
For your questions, an example of assonance is in the repeated o sound in the first line "Though I go to you." With that o sound, it seems drawn out, which makes the line seem longer, in a way, almost implying that the speaker is reluctantly wanting to whomever he or she is talking to.
An example of alliteration is in the last line with "waking world." The feeling that this gives is a bit harder to put into words. Since the poem itself mentions a dreamscape of some kind, the w almost implies white noise or lack of sound.
