My wife doesn't seem interested in sex. I'd like to ask her if there is anything I can do to help, but I don't know where to start. Any advice?
Communication is so important to a healthy sexual relationship. One study found that women who communicated well with their partner about their sexual needs had sexual interactions nearly twice as often as women who had trouble communicating. Those women were also nearly twice as likely to have an orgasm and were far more likely to actually enjoy sex. One such approach is exactly what you're suggesting: asking her how she is feeling about the situation and if there is anything that you can do to help. You may want to consider talking about sex and asking if there is anything in particular that she'd like you to do.
You can also consider taking her out to dinner in a quiet restaurant and tell her what you just told me: that you're concerned about her lack of desire and you want to help in any way. Do not make her feel guilty or as if she's at fault; instead, address this as a couple's issue and make it clear that you feel a sense of responsibility. This is also a good time to express your concern about her health and let her know that certain medical conditions or medications could be behind her low desire. Most of all, let her know that you love her no matter what.
Don't expect that this one conversation will resolve all your problems, however. The two of you need to keep talking. You may want to consider seeing a certified sex therapist. Sometimes a neutral third party can make it easier to discuss such intimate issues.
I also recommend that your wife visit her health care professional for a complete physical examination to rule out medications or medical conditions that could contribute to her low desire, such as depression. Your wife may have what's called Hypoactive Sexual Desire Disorder. This condition is diagnosed when a woman experiences a decrease or lack of sexual desire that causes her distress, may put a strain on her relationship with you, and is not due to the effects of a substance, including medications, or another medical or psychiatric condition. If everything checks out, she may want to talk with her doctor about approaches to improve her desire.