How do I enter college education expenses I made directly to my son and not reported on 1099-T?

You cannot claim a tuition credit unless:

1. Your son is your dependent

2. His school issues a  1098-T or you have a valid exception for not having one

The TurboTax (TT) interview handles all of this. 

In TurboTax (TT), enter at:

Federal Taxes Tab (Personal for H&B version)

Deductions & Credits

-Scroll down to:

--Education

  --Education Expenses

Follow the interview to completion. In particular, at the 1098-T screen, note the link "What if this is not what I paid the school" underneath box 1. There you will  be able to enter the actual amounts of tuition and fees paid. Later, you can enter books and other course materials. 

Money paid directly to your student son is not a qualified education expense. Only money paid to the school from any source (your, your son, scholarships, 529 distributions, etc) are qualified education expenses. The only qualified education expenses are books, tuition and lab fees.  That's it, with no exceptions.

If 529 distributions are involved here, then in addition to the qualified education expenses mentioned above. 529 distributions can also be used for the unqualified but allowed expense of room and board,  provide that room and board paid was "in direct support" of the education.

So if the student did not enroll as a full time student for the summer semester, room and board expenses paid for those months are not an allowed deduction.

It depends on what you mean by "I made directly to my son and not reported on 1099-T".

Your son needs to have received a 1098-T.  It doesn't have to show that YOU paid money.  It only needs to show that tuition was paid.  Likewise, you do not need to have paid tuition directly to the school.  If your student is your dependent, and tuition was paid, by any source, you can clam the tuition credit.  There's even a loop hole, where you can claim a tuition credit  for tuition paid by scholarship.