I have two SSA 1099 forms. One for my SS benefits (retirement) another one for child support as my son is still under age and going to school. Where do I enter form 2?

You only enter on your tax return the SSA-1099 that has your Social Security number in box 2 of the form. 

If one of the SSA-1099's has the Social Security number of your son, then you do NOT enter that form on your tax return.  If the child has no other income then they do not report the SSA-1099 on a tax return.

Are they both for you?  Then add them together and only enter the total.  If one of them has your son's ssn on it you do not file that one.  It would only go on his return if he has other income to report.