“(Insert legal gaurdian), what’s your opinion on trans people?”
If something like “they’re okay” or “I support” personally I’d say something like “what if, hypothetically, I am trans” and go from there. If they say something supportive, say something like “well, I’ve been waiting to tell you a long time” blah blah blah and if not supportive say “oh, well I was just wondering. You don’t have to worry about that”
And if not supportive answer with the first question, go to the “I was just wondering, since I read an article on (insert random trans article)” or something like that