Are you referring to Box 5 of a 1099-DIV? And your 1099-DIV has such an entry?
If so, when you go to the 1099-DIV interview to enter that 1099-DIV, after you enter the Payer name, it will only show you the first 2-3 boxes of the 1099-DIV; i.e., the most common ones. However, below those boxes is a small checkbox that says "My form has info in other boxes." Place a checkmark there, and the screen will expand with the additional boxes. And you should be able to then find Box 5, if that's what you are seeking, to enter the info.
The program will automatically calculate a QBI deduction and include it in your return.
NOTE: If you're trying to efile right now, be aware that one of the QBI forms (Form 8995-A) is supposed to become available in TurboTax sometime today 2/20/2020. The Form 8995 (QBI simplified computation) is already showing as available, but if you need the Form 8995-A, that is projected for today.
Addendum:
I added this note above in case you're wondering about the availability of one of the forms. You may have been emailed the above answer before I added the note. So here it is:
NOTE: If you're trying to efile right now and hitting a roadblock, be aware that one of the QBI forms (Form 8995-A) is supposed to become available in TurboTax sometime today 2/20/2020. The Form 8995 (simplified computation) is already showing as available, but if you need the Form 8995-A, that is projected for today.