How would you present your employment if you are working for a question and answer website like StackExchange (employer) and your job is to answer questions in a specific subject like Physics?
Such a person might have a job title: "Subject Matter Expert -- Physics" or "Physics Subject Matter Expert". Another job title might emphasize their role in the on-line community: "Community Leader -- Physics".
There are many other possible titles that are more fanciful and whimsical. For example: "Physics Guru" or "Oracle of Physics" or "Master Physicist".