Whatever what is, is is what I want.
That sentence is not in the poem. The actual sentence, which the question quoted correctly in context, was
what is is is what
Without the division into lines of poetry, but retaining the italics:
"Whatever what is is is what I want."
I believe the intended effect of putting words what is in italics in this poem is similar to the effect that could have been achieved by putting quotes around the words "what is": it allows this two-word phrase to be treated as a noun. Unlike the effect of italics or quotes in this paragraph, however,
the noun in question is not the phrase itself, but rather is the thing described by those words.
I might unpack the elements of that sentence in the poem as follows:
That which exists and occurs in this universe is what is.
Whatever that is, that is what I want.
I hope you agree that the two words what is were a much more fitting way to express the same thing I tried to express in the first eleven words in the previous paragraph.