Read James Brooks‘ answer to How do you enunciate the letter “W”? Is it “Dub-yoo”, “Dub-boo-yoo” or, “Double-yoo”? IS there a ‘proper’ way? It’s driven me berserk ever since phonics class in kindergarten. on Quora
While I pronounce it (using the International Phonetics Alphabet) /ˈdʌb(ə)lˌjuː/ (double-yoo I guess from your question) I would argue that there is no one ‘correct’ way to pronounce things such as words or letters. Many dialects and accents have their own pronunciations of words that are considered correct for their accent or dialect or area.
My mother (very neutral southern English accent due to moving around in the military as a child) pronounces it as I do (or rather I pronounce it as she does because we have similar accents) while my father (born Virginia, raised there and in Texas) pronounces it as /ˈdʌbja:/ (dub-yah I guess, and would enunciate it as such). They way they say it is correct for their backgrounds/regions/accents/dialects. They understand each other and the whole point of language is to communicate ideas.
If you look at the Romance languages, they usually say some variation of ‘double v’ or ‘double u’, so if you want to stick with one that is more widely recognised, that may be the one to go with.
If you want to learn more about the International Phonetic Alphabet, you can find a guide here: International Phonetic Alphabet and Phonemic Alphabets