Hi, Sharon! If I understand you correctly, you are concerned about asking your contacts questions that might violate overational security or that might make you look ignorant.
OPSEC is a huge deal. You are correct about them knowing what would be in violation, even though we non-military folks might not. I think they realize that we aren't up to speed on such things. Being honest with them about our ignorance is helpful. I've asked my guys questions and said, "I don't know if you can tell me this or not...if not, I understand." I try to never make them feel as though I am putting them on the spot. Often, they can't say where they are or what their particular job is. There is nothing we want to know that is worth risking putting them in danger by having them put out information that isn't meant to be shared. I have learned a lot since I began corresponding with my contacts but I am still a civilian and don't know everything. I don't need to know it all in order to be supportive.
I have been fortunate to have great contacts from whom I've learned a great deal. They have taught me how to be an effective supporter. I have always been honest with them about what I understood and what I was clueless about. I think they appreciate the fact that those of us who are ignorant want to know more about our military and how they function. I'm not talking about things that are of a security sensitive nature, but just things like how often they go on R&R, who goes when, what's the difference between someone in the reserves and someone who is regular Army... Those are a few of the things I've had the privilege of learning over time.
As far as figuring out what they specifically need, that is a never ending project for all of us here. Some contacts tell us in their posts, some in their emails or letters. Some don't tell us much of anything - either because they are short of time or they just don't want to ask for anything specific. I've learned that it doesn't hurt to ask. If they can tell us and want to, they will. If they can't or don't want to, they won't. I had one contact that I sent a questionnaire to and he checked off a list for me. I can email you that list if you want to look at it to get some ideas.
I hope I answered your question somewhat. Let me know if I didn't and I'll take another stab at it. I appreciate your concerns and applaud you for wanting to "do it all right" - just like we all do. 