Should I report income earned via a cashback/games mobile app (BenjaminOne)? And if I should, how would I file that?

Yes, income earned from an online app should be reported as taxable.

 

If your earnings were part of a business activity, you would include them with your Schedule C self-employment. If this is not part of a business activity, you can report this as Other Income:

 

In TurboTax Online:

 

1. Sign into your account, your return, and click "Pick up where I left off
2. Click Federal
3. Click Wages & Income
4. Get to All Income and scroll down to Less Common Income and click Show more
5. Scroll down to Miscellaneous Income, 1099-A, 1099-C and click Start
6. Scroll down to Other reportable income and click Start
7. Type a description (such as "cashback app income")  into the description box and enter the amount