Yeah, asking is the best course of action - at least that way it cuts out any ambiguity. It can get pretty confusing for even trans people as to what other trans people want to be called. There are some who ID as trans but are fine with their biological pronouns, others hate their bio pronouns. I even knew one trans person who was more generqueer and insisted on people using he and she in alternate order, often in the same sentence. That one kind of went down like a lead balloon, because there are limits.