It's easy to know who cares.
They reach out with words and kind gestures. They ask questions and respond to questions. They demonstrate care and concern with regard to your interests, efforts, desires, and challenges.
Some simply don't care. They don't have time for you and they are not interested in your pursuits or efforts. Frankly they'd rather that they didn't have to spend time with you, work with you, or problem solve with you. Most people are somewhere on the continuum between interest and non interest when it comes to your life.