The small linking sound /w/ is written o before a, ă, e (hoa, hoặc, hoe) and u before the other vowels (huế, tuy). After q it is always the u of qu, written once: quan sounds like toán, quân like tuần.
hoa · hoặc · khoẻ · huế · tuyết · quan · quân
Quick answers
How do you pronounce Tuấn?
Block by block: â → n → ân → uân → t → tuân → sắc → tuấn. Tone: sắc (acute accent · high rising). Read each block aloud, then compare with the recording, in a Southern or a Northern voice.
What tone is Tuấn?
sắc (acute accent · high rising)
Is Tuấn said differently in the South and the North?
South · Sài Gòn: uân = uâng. North · Hà Nội: said as written.
What does “tuan” mean without the marks?
Without the marks, tuan can be several words: tuần (week), tuân (to obey). The marks decide which one.