1. Questions about purpose
Questions about purpose many times are "why" or "what" questions like; Why do we do this exercise? We can ask this same question as; What is the purpose of this exercise? Another good question about purpose is; Why should we do this or that practice?
2. Questions that give some background
Questions about background can come from a number of different angle with different approaches. If we have some background many times it can give us some insight to the practice we are asking about. Personally I am amazed that more people don't ask me about what I do or don't do... practice or what I have done or what I may have discovered about a certain practice when I did them. Then a great follow up question would be why I do or don't do certain things. Also a basic history about a practice or where they where developed or how they were developed can sometimes give insights to a practice too.
3. Questions about stages and results
Questions about what we might expect when we practice. These are always good questions to ask about. If we can gain some insight about what results we should look for or what stages or levels there are to a practice this can give us some idea of what to look for... Actually even asking that question is a good one; What am I looking for when I practice this? What are the things I can expect from practicing this? Are there different stages of practicing this?
The one word of caution I would give is to try to understand where you are at when you practice. So, if you ask about stages or levels of practice you may want to also ask; What level should I practice at? The reason I say this is because so many people want to practice at stages beyond their skill and the end up not getting very much from the practice. It is always good to work at basic levels and get a good full understanding before moving on to more advance levels. Even when you get to more advanced levels it still good to go back to basics often. I will also say sometime certain people can be afraid to take the next step or practice at the next level. This can also be a good topic to ask about.
4. Questions of how to do something
Questions of "how" are questions of instruction as in the question; How is it done? How do I get this part to do that? When I do this how do I do that? These questions are questions looking for advice on the practical workings most of the time and are good questions to ask. But, if you don't ask some of the questions above you might not have the depth you could have when practicing and really be limiting yourself.
Note: One more thing about questions
It is good to ask yourself these kind of questions too. It is good to ask yourself these kinds of questions often. By asking yourself questions you open a door in your mind that starts to seek for more, a deeper knowledge and understanding, with this knowledge and understanding you can start to get a greater awareness of what you are practicing. Once you gain these understandings and an awareness to some degree you can start to develop a better "feel" for what you are practicing and doing... which will lead to new and deeper questions to be explored and asked.