hangouts - How to see the properties of my partner to a discusson? It must be a simple question.

I'm chatting a while with the man. I have his contact in hangouts program (I have not his contact in my phone contacts). 

I have added this chat by email. Now I want to see the email.
The email is the main identifier, and it must be there.
The question become principled.

It is so complicated, I can't figure it out.
How can I find the email of contact in hangouts?

Thank you, in advance.
To get your interlocutor mail adress in Hangouts, go in the conversation, then click on the 3 dots (top right corner), then Partcipants and Options (not sure about the translation) now click on the green circle at the bottom of your screen and your contact's mail adress chouls appears.

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