A good inquiry begins with an inquiry-style question. If it would be easy for you to find and understand the answer to a question, the result is not really an inquiry, it's just "looking up the answer." On the other end of the spectrum, "how do I learn to read music?" suggests an important long-term goal, but it is too broad a question to be answered in just one inquiry cycle.
A question is a good starting point for an inquiry if it takes you into slightly unfamiliar territory, where understanding will take a little effort. What constitutes a good question therefore depends on you. Consider, for example, three people who hear the term circle of fifths and decide to look it up. One has never studied music, cannot follow the explanation, and gives up after a frustrated attempt to understand what "fifths" are. Another has played piano for years and quickly recognizes that the term refers to patterns that he had already noticed when practicing scales. The third is a beginning saxophone student who has to puzzle through the circle by comparing it to the major scales and key signatures that she knows, then uses the circle to predict and play through some scales she has not yet learned, and from there decides to try to understand the "relative minor" scales that are also part of the circle. All three people had the same question, but that question only led to an inquiry in the third case.
If you do not have a clear idea of the goal of your inquiry, or of a question that can get you started off in a first cycle of inquiry, you may want to do the inquiry in the Designing Inquiry Questions module.