On the Form SSA-1099 for your son's Social Security benefits, the Beneficiary's Social Security Number in Box 2 at the top of the form should be your son's Social Security number.
You do not report your son's Social Security benefits on your own tax return. It's your son's income, even though it is paid to you. If your son files a tax return, he has to include his Social Security benefits on his return. If the Social Security is his only income, he is not required to file a tax return and his Social Security does not have to be reported anywhere.