If I earn money on PredictIt.org, but it is too little for PredictIt to send me a Form 1099, am I obligated to report it in my federal tax return? Let's say I have net earnings of $10 for example.
From the instructions to form 1040:
Generally, you must report all income except income that is exempt from tax by law.
There is no minimum (for a single source) under which the IRS no longer cares except if you make so little money in total (over all sources) that you don't need to file taxes at all.
You can double check the many exceptions in publication 525, but nothing comes to mind. You may be able to use other losses to balance these gains.
I am not familiar with "Predictit", but unless this falls into some special category that makes it exempt from Federal taxes, then the short answer is, Yes, technically you are legally required to report it.
Consider a retail store. They may make thousands of sales of just a few dollars each. They are most certainly liable for income tax on these sales. Even though the amount of each is small, they add up to a big amount, and there's no way the IRS is willing to miss out on that revenue.
I suppose in practice if you fail to report $10 in income, the IRS is unlikely to ever find out, and they probably won't devote a lot of resources to tracking it down. But the amount of tax you owe on this income is pretty small too. Is it worth the potential of getting into legal trouble to say $2?
I'm not a tax lawyer, but I'd guess it would go on your 1040, line 21, "Other Income". This line is for prizes, gambling winnings, etc.