If your 20 year old son was a full-time student in 2018 then you can claim him as a dependent. You should get the $500 credit for other dependents for him--as already noted above. You can also enter his education expenses on your own tax return--so if he has a 1098T enter it on your return.
Go to Federal>Deductions and Credits>Education>Expenses and Scholarships
The amount of money your son earned while he was a full-time student does not affect your tax return., nor do you enter it on your return. He can file his own tax return in order to seek a refund of tax withheld, but he MUST say on it that he can be claimed as a dependent on someone else's tax return.
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