Is he exempt from US taxes on income earned in a foreign country?

[Jurassic Park Dino]

My friend has just asked me this question. I am not quite sure how to answer it. His grandpa is 74 years old who receives annuity payments and social security benefits. Recently he lived in a foreign country about a month & earned some income. Is his all foreign income taxable? Thank you.

[esnagel]

Once again, I'm not certified to answer this question...

I receive income from another country and I have to claim it. If your grandfather lived in another country, earned the money, and spent it there, I don't think anyone's going to find out. But if he brought some money back with him, he may have to claim it.