Before we get started, let's get something straight: an informational interview is not a job interview.
Even if you're not currently job searching, requesting an informational interview with someone you admire (or with someone whose job you admire) means you're willing to meet with them to hear their story without pressing your own on them. Informational interviews are an incredible way to get a clear visual of an industry, company, or position to determine if it's right for you. When done right, they also help you expand your professional network (and yes, many people have received job offers because of an informational interview they did).
Here are some general questions that should work well regardless of industry or the person's professional background. Just make sure that they're relevant to the person by doing thorough research on their work in advance. Dive in!