Where can I see in fortnite who I gave away things to? Can someone

Fortnite

I don't think so

You can't see this anywhere and why shouldn't it help?

Certainly that brings something, so… Brief explanation, my son lets his friends on his fortnite account and suddenly 20 euro (2000 v-bucks) are gone, he has not bought anything himself. His friends can then buy things and send them to themselves as gifts.

Unfortunately, there's nothing you can do about it, the 20 euro are gone, it is best to ask your son which friends they are and clarify this with the parents. And if you change the account's password, this can no longer happen. And good friends wouldn't do that.

This is exactly why you shouldn't let your friends play on your account and certainly not when v bucks are on it.

You should tell him that he should give you access again.