Don't you
Doncha
/ˈdoʊntʃə/AssimilationReduction
In real speech
What happens to the sounds
t + y blend into /tʃ/ (“ch”), and you weakens to /ə/: don't you → “DON-cha”.
When to use it
Doncha think…? Doncha wanna…? Common in songs and fast speech.
Casual → formal
Slang
doncha
Neutral
don't you
Formal
do you not
Sound notes
Assimilation: neighbouring sounds change each other, e.g. t + y → “ch”, d + y → “j”.