When im trying create an account with my username, system says "already taken"

How can I see which mail using my username or how can I see the accounts in GOG ?

Why not just go for a different username?

Now, now. Don't come hunting down that other use whose username you want.

Ah, it's not your username, you see. It's just a username anybody can use if it's not already taken.

You can't, there is no way GOG are going to show you an email address associated with a username, for security reasons. And you asking about that makes you look very suspicious.

Why are you even wanting to know? Have you forgotten your password maybe? Just do a password reset along with the email you have previously provided.

"Already taken" simply means, that some other user uses the name already, which you want to use.

Usernames are delivered on a "first come, first served" base.

And no - you can't see the email addy of the person who uses your wanted username.
Why would you? It's taken - and you obviously have another one already (DoctorHuhu).

And only to elaborate a little bit further:
if at any point in the future, any other person comes along, wants to create a GOG account, and wants to use the name "DoctorHuhu" - they can't.
Because that name is now yours.
All that person can do is to either choose a different name, or to add something to that name (e.G.: DoctorHuhu123).

Edit: typo

DoctorHulu is a terrible commando name. Why not pick something like Firebert?

Or DoctorHaha, DoctorHihi, DoctorHoho, ...

I think those fall under the category: "choose a different name".

There are no free rooms those days ^ You will be asked to stay home ^ :D
Doctor Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn

to look for a person: Friends--> Invite New Friend--> start typing one letter at a time Yes and no too. It is a chunk of a complicated process, but, they can switch their names with each other if they want to. (I know if the other person mutually wants it too)

Something like DRM-free usernames? :) Cheers

Or Doctor_Who...

You better run.

Run into the mystic night.

You can't... because that would be a huge security flaw.

So let me get this straight: OP is falsely asserting that someone else's username is his username?

The OP is worded in a way that gives a very misleading impression, as if to imply someone stole OP's account, which doesn't seem to be what actually happened.