As far as I know, Shaytan whispers in our ear and cause to do things which are not permissible or which causes damage to our deen, but can he hear what we are thinking or planning in our mind and misguide us?
This below is my opinion. I haven't read it anywhere. Satan can't read your mind. Only Allah knows what is in your mind. But he can read your emotions. For example you can be angry and he starts playing with your emotions. All physical change can be read. because he has observed us for billions of years. He can cause some physical changes. For example, he can make you to forget some things, or he can make you to think of bad deeds, if you are angry at someone he would make you angry when you see,hear about that person. Whatever happens you need to say Bismillah. Remember if you don't do that bad thing you get one sawab. PLease take a look at https://www.youtube.com/playlist?list=PLD27509EA7EE1FD7C. you can search for word satan and see all videos. Hope it helps