Do I have to report "medicare tax withheld" in box 6 of W-2 ? If so, where do I report it in my income tax return?

Don't you see box 6 Medicare on this screen?

Thank you so very much!

It goes on the same screen where you enter the W2.

To check your W2 just type w2 (small W) in the search box at the top of your return and click on Jump To the W2

Or go to…..
Federal Taxes Tab
Wages & Income
You should get a box listing all your W2s.

Then click  Edit by your W2 to double check it or change it.