My son has SSI he has a judgement against him he has no assets and his only income is the SSI, can they take money from his SSI payments?

Only the feds can garnish federal benefits but creditors can freeze any bank accounts in his name pending further court actions. There is more here.

https://www.consumer.ftc.gov/article...deral-benefits

It can be a lengthy and expensive process though, involving lawyers court and judges once a bank account is frozen.