"Don't you want to go" assumes that they DO want to go. "You need to drive faster to stay on schedule. Don't you want to arrive on time? Hurry up!" "Do you not want to go" is much rarer, and could have 2 different meanings, depending on context. A) It could assume that the answer is "no, I do not want to go" "Why won't you marry me? Do you not love me? Do you want to break up? Is that it? Answer me!" B) It could be very formal and romantic, like something a nineteenth-century poet would say, but have the same meaning as "don't you". "Do the stars not shine above us? Do the night birds not sing sweetly? Come, then, and dance with me through the beauty of the night."