Turbotax says: Tell us if any of the $ in Box 5 of my 1098-T includes amounts already reported as income on my W2. What does this mean? Should I choose yes or no?

This question is asked to find out if your employer is reimbursing you for your tuition. This would be reported on your W-2 if the tuition reimbursement was above $5250. 

The IRS instructions for Box 5 are:

"A scholarship or grant is administered and processed by you if you receive payment of an amount, whether by check, cash, electronic transfer, or other means, and such payment is designated as a grant or a scholarship by the payor, or the circumstances make it clear that the payment is a grant or scholarship. A Pell Grant is an example of a grant administered and processed by a college or university in all cases."

Therefore if you received a W-2 that has amounts designated for your education "ONLY" and these represent amounts that the college or university is reporting on your W-2 (for example reimbursement for course work that you completed and paid out of your own funds that your employer had previously reimbursed you for, those amounts MAY appear on your W-2 and thus TurboTax needs to know what those amounts are so you do NOT count the income twice (and thereby increase the amount of tax that you will need to pay).

Hope that helps

If your 1098-T DOES NOT report any payments made by your employer, answer "No". 

It is not common, but sometimes an employer will pay tuition to a school for their employee. 

@ctnozdmr