I cannot figure out what items were added for line 17 of my return. The IRS cannot figure this out either.

2019 1040 line 17 for withholding?  That comes from from any W2 box 2 and 1099 box 4.  So add those up.  If you have a lot of investments or high income there is an Additional Medicare tax on Schedule 2 line 8 which goes to 1040 line 15.  That is offset with an extra amount on line 17 with withholding.

If you saved a PDF of the return with the worksheets then look for the line 17 worksheet for your answer.  If you did not you will need to either wait until December  to download a fresh PDF   OR  used the amendment process to open the return using a downloaded program.