Nintendo Network ID 3ds?

I found my old Nintendo 3ds and want to transfer my data to my new Nintendo. On my old Nintendo, I never confirmed the Gmail address, and I forgot my password. I also do not know where to see what the Gmail address is. I forgot that too. Can someone tell me where to find out what my gmail address was?

Are you still logged in to the phone with your Gmail account?

I do not know. I sent a message to this Gmail address, but nothing came. I do not know where to see which Gmail is logged in