Formal:
* Хотите кофе? (Khotite kofe?) - This is the most formal and polite way to ask. It literally translates to "Do you want coffee?"
* Не желаете ли кофе? (Ne zhelaye li kofe?) - This is a slightly more formal and polite way to ask. It literally translates to "Wouldn't you like some coffee?"
Informal:
* Хочешь кофе? (Khochesh kofe?) - This is the informal way to ask, using the familiar "you" (ты). It literally translates to "Do you want coffee?"
* Кофе будешь? (Kofe budesh?) - This is a very informal way to ask, using the informal "you" (ты) and a colloquial expression. It literally translates to "Will you have some coffee?"
Offering coffee:
* Я предлагаю вам кофе. (Ya predlagayu vam kofe.) - This is a polite way to offer coffee, meaning "I offer you coffee."
The best option for you will depend on the context and your relationship with the person you are speaking to.