Hello, I am a naturized U.S citizen and want to apply my girlfriend for immigration to US as my wife. She is holding J 1 visa and staying in US right now. What do I need to do next, and how much income should I have to sponsor her? Many thanks

Since she is a J-1, check to see that she is not subject to the 212(e) two-year home residency requirement. It will be noted on her visa and the DS-2019, if she doesn't have a copy, the program RO will.

If all good, then you need to qualify income wise at 125% of the HHS poverty guideline. Check the I-864P for the breakdown by family size.

Verify all this with an experienced immigration attorney. Congratulations and good luck.