I'd guess Ts are mostly left wing, although I can't be sure.
I think if they're working with the less privileged people and care about them, they'll probably vote for more "humane" party. But it's really hard to say. I also know a psychologist (my ex classmate) who's right wing.
I guess you could try to guess based on their other interests and random comments.

I've also wondered about my T and I've got an estimation based on what she's told me. If I'm right, she is the same side as me (left). But this is enough for me, I won't ask as it's not crucial to know. However if it is important to you, I'd risk and ask your T. If could be an interesting conversation. I'd go for it.