There is no deduction for a contribution to a Roth IRA.
To make an IRA contribution (traditional or Roth) your son would have to have income from working - wages or self-employment. If he has income from working, you cannot report his income on your tax return. If it is reported at all, it has to be on his own tax return.
A Roth IRA contribution does not have to be reported on his tax return, since it is not deductible. If his income is so low that he is not required to file a tax return, then there is no need for him to file because of a Roth IRA contribution.
(There is a retirement savings contributions credit, also called the Saver's Credit, for IRA contributions, including Roth IRA contributions. However, since your son is a student and he is your dependent, he is not eligible for the credit.)
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