This question reminded me of what I said when I participated in some qualitative research a while back. I was asked what I, as an adoptee, would want a therapist to know if they served an adopted client. I will tell you what I told them, with some finessing of course now that I've had more time to think about it. Simply put, I said,
Whatever you think you know about adoption, it doesn't matter. What matters is what the adoptee thinks about adoption.
It is necessary to be culturally competent to serve a diverse population. If you serve anyone who is different than you are, who has experiences outside of your own, it is vital to find good information as a way of empathizing with their experience. Therapists serving adoptees are included in this and adoption research and theory are out there. These areas need to be explored.
But I think the most vital act of kindness is not to cast judgement when someone shares they are adopted, it is not to make a disapproving--or even approving--face. It is not to tell a grieving person to hurry up and shut up. It's said this is why we subconsciously start looking for tissues when we see a person crying. We are looking to find quick comfort--to what might be a world of pain manifested in just a few tears. Being handed a tissue can signify to someone that it is time to stop crying now. Sometimes it's best not to offer one right away--a good cry can help from time to time.
If you want to help someone, start where they are. Not where you think they should be.
Sometimes, the best thing to say is simply, "Tell me more."
Not everyone knows this or communicates like this. Which is why it's always good to have a good support system in close friends and even fellow adoptees. This is what I as an adoptee would want from someone attempting to help me. This is what any person being helped deserves. Adopted or not.