Hello, I'd like to help you with your question.
When there is an issue with sexual desire, the first step is to rule out anything physical that could be wrong. Talk to your wife about seeing her doctor to rule out any reason why she would not desire sex. It could possibly be a hormonal issue depending on her age. If she is close to menopause or over the likelihood the cause is hormonal increases. If she is younger, that is more unlikely, though there are other causes. It is possible that your wife does have a physical issue and either is fearful of addressing it or feels embarrassed to do so.
However, if there is no physical issue found, then your wife's issue is most likely emotional. Possible reasons for a lack of sexual desire are depression, anxiety, certain medications, stress or trauma of some sort. To find out why your wife does not desire sex, it would be helpful for her to have an evaluation by a mental health therapist. The therapist can do an evaluation to determine if there is an emotional reason and if so, what to do about it. Therapy can be very effective with addressing sexual issues.
In the meanwhile, talk to your wife about how you feel. Do not ask her for sex but instead just talk. Oftentimes, for women, sexuality is highly connected to emotions. So you may want to be open and encouraging towards her to share anything she feels about your marriage. Also, talk to her about other ways she can show you affection until the issue around her sexuality can be resolved. Find ways to be closer and show your love for one another. This may trigger her sexual desire and help her connect with you. Try asking her to do small things to express her feelings about you.
Also, ask her if it is possible if both of you try to work on this issue together. Take it one step at a time. Learn as much as you can about rekindling sexuality. Here are some resources to help you:
Wanting Sex Again: How to Rediscover Your Desire and Heal a Sexless Marriage by Laurie Watson
The Sex-Starved Marriage: Boosting Your Marriage Libido: A Couple's Guide by Michele Weiner Davis
The more you know, the more tools you have to help your relationship.
I hope this has helped you,