My son's parental rights were terminated and I adopted his daughter, soon after, the friend of the court started garnishing his wages for child support. If he's not legally the parent, how can he be responsible for child support. He never sees and doesn't know his daughter. I am legally responsible for all aspects of her life. Also, if I opt out of child support, will they continue to take his wages and just not give me any, or will they stop.

The child was adopted... legally all responsibilities of his ended at that point. He needs to get a lawyer and have them present all the documentation proving the adoption took place.

There is a chance someone didn't "get the memo" and are operating on the assumption he is still legally the father. A lawyer should be able to get the right motions filed to end it...The assumption being he was current and up to date at the time of the adoption.....if he was in arrears at the time of adoption...that ammount would still be owed.

Or there could be old child support due. Perhaps the son has not notified them of the adoption?

You are correct that a legal adoption ends any future support obligation. So either you got custody and not an adoption (they are different), or the court is not aware of the adoption, or they are collecting back support.

Has anyone talked to the "friend of the court" and asked why they are taking support payments? Are you getting those payments? (if so, there is nothing stopping you from returning the money to him.)