which one is correct?

[Titoo]

Hello,

please tell me which sentence is correct? (or may be both, or none??)

"Which country you prefer to live in?"

or

"In which country do you prefer to live?"

thank you in advance,

Titoo

[Casiopea]

"Which country do you prefer to live in?"
"In which country do you prefer to live?"

Welcome, Titoo.

Both are acceptable. There's an old (prescribed) rule which states, "never end a sentence in a preposition (e.g., "in"), but that rule doesn't apply to Modern English.