Controller on a PC ( how to activate the chat window!? )

Hello!

I searched a lot in game and over the internet. I cannot find a list of hotkeys anywhere ( for controller)! for example I want to use the IN-GAME CHAT!! But the game doesn't tell me anything about how to open the chat window. Same with answering to whispers; I simply cannot reply back for trades and friends!

WHat key do I need to press to activate the chat window ( with controller active ) please!?