How do you investigate diocesan priest without attending service there? Do you make an appointment with the parish secretary? What do you say it's about?
Different ways. Google, parish website, asking around, and trial and error. Sometimes I've just gone to confession to them, and really, I'm just looking for absolution and the correct form, if they say something silly in giving advice, I just politely disregard-- he can't see me anyways. If he is truly, just confused and indoctrinated but still a Catholic he will use the correct form, albeit in English. If he uses the incorrect form, I would just not go back and I'd make another confession at another time like that one never happened. I've actually found some wonderful priests tucked away in their 70s, 80s, 90s here and there, I prefer them to traditional priests sometimes.
If I need spiritual advice, I normally a traditional priest, a moral theology manual, or a good book, I don't bring it up in confession.