I'm from Europe and I wanna give someone from the US a PSN gift card. How can I do that?

Unfortunately, the PSN does not support buying games as a gift.

Fortunately, gift cards exist, and Amazon sells gift cards as digital code.

Here are a number of things to keep in mind:

• These codes only work for regions that use the same currency. EUR for Europe, USD for US, JPY for Japan, etc.
• The PS4 is not region-locked, so there's no guarantee that person is actually using a US account, even if they are using a US PS4. The probability is high if they were born and raised in the US, but if they moved from Europe, they might be using a European account instead. Check with them to ensure you don't buy the wrong gift card!
• According to a comment on Amazon, it seems these gift cards can expire if you haven't redeemed the code for some time after purchasing it. Make sure the person you're gifting to is aware of this and redeems the code as soon as possible.
• According to some other comments on Amazon, it can take a lot of time until you actually receive the code. Make sure you don't buy the gift code at the last minute.
• Don't forget to check if the card you want to buy is actually available.

If you do not trust Amazon, you can also buy a physical gift card instead and have it delivered to that person's home address. The same rules about regions still apply to the physical cards. Do not buy the wrong ones! It's also safe to assume that physical cards expire as well.