This is your preemptive warning that someone will come along and suggest Eric S. Raymond's "How To Ask Questions The Smart Way". DO NOT FOLLOW THAT ADVICE.
When you approach someone with a question, it's because you believe they have understanding you do not. So lead with that, "hey, I hear you are the go-to person for questions about...", and give the person an out to say, "no go ask so-and-so" if they aren't willing to answer.
If the person says, "I don’t understand the question" without following up with questions back to you for clarification, take that as a tacit admission of ignorance, and go elsewhere for answers.
Be careful of your wording. I know I am guilty of this at times, phrasing my questions in a way that can sound provocative. This is a judgement call, you have to have some awareness of what might provoke the person you're asking.
Be respectful of others' time. Don't "blurt" questions to someone just because they are handy. Ask for time, say, "when you're at a stopping point", and let them turn their full attention to you and your question.
Remember the adage, "He who asks a question is a fool for a minute; he who does not remains a fool forever."