The more open you are about what you want, the more comfortable she will feel. If she suggests something, ask for specifics: when and for how long are good places to start. Soon she'll be describing exactly what she wants you to do to her (and ideally in vivid detail). Talking about sex with a partner can sometimes be the best part of the entire activity. OK, second-best.
Once this discussion gets going it can be sexy enough to inspire another round; which, with your recently acquired knowledge, is going to be better than the first.
What if she doesn't know?
What happens if you've asked the question but she doesn't have an answer? Keep asking. Don't harass her, obviously, but check in occasionally to see if there's anything different you could be doing to make her feel good. Maybe she's genuinely satisfied, but more likely she's working up the nerve to tell you about her sexual preferences.
If you're in a committed relationship and she's uncomfortable discussing this with you, consider whether there's a problem with your communication in general. For couples that have sex, it's a fundamental part of the relationship and something you should be able to talk about honestly.