You may get information from only your own tax return. Even married couples who do not file jointly are not allowed to receive information from the other spouse's return.
You should file your return as it is legal for you to do even if another person DID claim the child which is rightfully your dependent. IRS will review both returns when this happens and only one claim will be honored. Any refund will need to be repaid to IRS if that taxpayer's claim is not valid. Penalty and interest may also accrue from the due date of the return until it is repaid. Earned Income Credit may also be subject to limitations for the false return which could affect that taxpayer for up to 10 years.
IRS does not have the information available to view the return.
Your son can go to www.irs.gov and click on the link for "where's my refund". He will need the filing status and amount that he was told was his refund. If the amount is not correct, he will be denied that option.
He can also go to his local IRS office to view the transcript (figures but no actual return) with an agent.
He can send Form 4506 to IRS with a fee of 36.00 (may have increased) to get a copy of his filed return. Form 4506T will give him a free transcript of the figures for the return.
One important fact is that HE must have signed the return and not anyone else. To file his return without his signature can be catagorized as a felony. IRS is very interested if this is the case and they will pursue it quite actively at no cost to your son.