The way to know if you are special to someone is to simply observed how they treat you. Do they treat you with respect? Do they listen to you and support you? Are there moments of spontaneous emotion/connection between you, be it laughing hysterically or painful tears? Just observe.

Specialness doesn't have to be exclusive to you for it to be real either. I have many relatives and they are all special to me in very individual ways. I have three children. One is not more special than the next, rather we have our unique special relationships. I have had many, many students over the years, some of which are particularly special to me for a variety of reasons, but none of them is "most" special that I can think of.

Rather than hope for being THE most special client of your T, find the unique specialness that lies between you and value it for whatever it is. You can do that yourself; you really don't need to ask, though I suppose you can if you want to. But perhaps being able to find your own specialness for yourself would be the greatest gift to yourself.