multi is right - the very best way to find out what an alter is thinking is to ask them.
Because of the nature of alters, we multiples have to develop internal social skills. We have to get to know those individuals much the same way we would get to know an "outsider" - Slowly, and with respect.

Just the same as we do not like everyone in the outside world, we may not like everyone on the inside. And they may not like us. I am starting to learn that the secret to internal communication is to work along the same social lines as I would with any outsider. I demand that I be shown respect for one. And I also show them respect. I allow for difference of opinion. And I say "Hello" when I sense them close to the switching point. And I ask them how they are doing.

Just by doing these things that sound simple, we open the doors to internal civility!