Where is the Tax Computation Worksheet? Or, where can I see where TurboTax computes the income tax on ordinary income?

Click on Forms in the upper right corner.

Where can I access the "tax computation worksheet" in the TurboTax desktop version?

For the Desktop version you can switch to Forms Mode and open the worksheet to see it.  Click Forms in the upper right (upper left for Mac) and look through the list and open the Qualified Dividends and Capital Gain Tax Worksheet.

Not every tax return has a "tax computation worksheet". For most people, Turbotax simply looks up the amount on line 10 of form 1040 in the tax tables, to determine the tax that goes on line 11 of form 1040.