Can I sue my employer for wage discrimination? How?

Yes, you may sue any one for anything. But, will you win? I do not know enough facts to tell you if you are likely to win. You did not state the basis for the suit. I recommend you consult with an attorney. If you have a good case, they will likely charge you only if you win, and you are more likely to win if you have an attorney. Go back and look at the question, you do not even know how to file a suit, much less what should be in that suit.

Contact the Wisconsin Equal Rights Division, US Dept. of Labor or an attorney.