My nephew got put in foster care but the court ruled he will be adopted because my sister was an unfit mother and the father is nowhere to be seen.could I adopt him and if so how would I go about it?

Start with a lawyer.

Depending on the complete reasons he was removed from your sister's care, you may or may not have a chance.

Even adopters (or should I say "especially" here?) through the foster care system need to go through a home study and all of the other steps to adopt.

I would start by going for guardianship first.

Please realize that part of the reason that children removed for abuse and neglect are NOT returned to family members' custody is because the idea is that you "let" your sister abuse/neglect the children.

In any case, you NEED a lawyer. There's no way you are going up against DFS without one.