Can usually tell how people are feeling on the surface, by their behaviour. Coming from the sort of background I did, I can enter a room and sense/interpret the psychological temperature of most of it's occupants. It doesn't mean I can do anything about the people in the room, it serves as pre-warning related to my own self-preservation.
I have difficulty with people who hide their emotions, who don't in some way broadcast them. Yet I can usually tell that they are hiding them by the confusing signals they show. I end up confused, and that's the sign for me, to tread lightly. Have been told by people close to me, to stop interpreting their emotions, often they are not even aware of what they unknowingly broadcast, and will deny my interpretation. It's takes a lot of energy to do this and I'd rather not automatically enter into someone's reality.
But empathy, I do have no matter what I've read about Aspies, we don't all fit the strictures of the DMV. It's a learned skill, it's clues are behaviour, eye and face movements, hand and arm and leg and foot movement. The manner in which someone sits, looks, talks, walks, how they place their feet. How they dress, what they say and don't say, what and how they eat, what they like or don't like. What they choose and don't choose. If you study human beings enough, you begin to see patterns. One person is pretty much like another, give or take a few differences. Although that doesn't usually apply to Aspies, who are completely different from others I've known. It requires that you decide how you would feel if you were them, like an actor, that you can emulate, and the resultant emotions you would feel.
I know when people feel a certain way, and can express sympathy, yet I feel false doing so. As if I'm uttering meaningless words. Often, I know the required script, to comfort others. It doesn't mean I like doing so, it usually means that it's easier than becoming too involved and affected by their emotions. Once I've expressed the learned phrases, it's over. And I'm on my way back to my world.