Who does your child live with? Which one of you did he spend the most nights with in 2020?
If your child does not live in your home more than half the nights of the year, you can’t claim your child as a dependent unless the other parent gives you a signed form 8332 dependent release. This form will include the child’s Social Security number. If you have a court order that requires the other parent to give you this form this year and they are refusing, you have to go to the Family Court to get the order enforced. The IRS will not allow you to claim the child without the form. If you go to family court to enforce the order, also ask the Family Court to turn over the Social Security number.
If you are the parent who has custody more than half the nights of the year, then you can claim the child as a dependent without the other parent‘s permission, but you do need the Social Security number. You may be able to take the divorce paperwork and the child’s birth certificate to your local Social Security office and get a copy of his Social Security number. Or, you can go to the Family Court and ask that the court force the other parent to turn over the information.