The IRS asked us to provide Form or Schedule 2 to support Line 23. Where does the info from Line 23 of the 1040 come from? Same question for Line 13. Thanks!

1040 line 23 comes from Schedule 2 Additional Taxes.  Could be Self Employment tax.  Here is IRS Schedule 2.  Yep you might have self employment income if you have a QBI business deduction on line 13.

https://www.irs.gov/pub/irs-pdf/f1040s2.pdf