We installed replacement energy efficient skylights at our second home for about $2,500. Where do I enter the info?

You can enter them in the Deductions & Credits section:

1. Open or continue your return, if you don't already have it open.
2. In TurboTax, search for energy improvements. (Don't search for energy credit as this will take you to the wrong place.)
3. Click the Jump to link in the search results.
4. At the bottom of the Energy-Saving Home Improvements screen, answer Yes and continue. Follow the instructions.

It says skylights are qualified but in the choices listed under "How much did you pay" it says insulation material, expensive exterior door, all other exterior doors and exterior windows." I don't see "skylight".

Yes, windows and skylights are entered on the same line that is labeled "Exterior Windows" in TurboTax.

Here's how to enter that in TurboTax Online:
 

1. Sign in to your TurboTax account.
2. Select Deductions & Credits, then select Start or Edit to the right of Home Energy Credits. 
3. Answer the questions on the next few screens according to your situation.
4. Continue until you get to Tell Us How Much You Paid for Energy Efficiency Improvements.
5. Enter your expense for energy efficient skylights in the box to the right of Exterior Windows. 
6. Continue through the remaining questions in the section.