If I have a single member LLC that received a 1099-INT, where do I report that on the tax return? On Schedule C? or on Form 1040 Line 8?

Since you are a sole proprietorship, report the interest from the 1099-INT on the personal side of the return--1040, line 8.

To enter the interest in TurboTax, please follow these steps:

1. Click on Federal Taxes > Wages & Income  [In TT Self-Employed:  Personal > Personal Income > I'll choose what I work on].
2. Scroll down to the Interest and Dividends section and click on the Start/Revisit box next to Interest on 1099-INT [See Screenshot #1, below.]
3. If you haven't already entered interest, continue through the screens, entering the requested information.
4. If you have already entered interest, you will see a screen Here's the interest we have so far.  Click on the Edit box next to check entries you've already made.  OR click on the Add interest income link to make a new entry.  [Screenshot #2]
5. You can choose to import your bank or brokerage statement or choose I'll type it in myself.
6. Enter your interest on the next screen -- Let's get your 1099-INT or brokerage statement details. [Screenshot #3]