That means showing and telling. So, if she doesn't volunteer the information, then you should ask. In fact, the more you ask, the more attentive you are, and she might like that. They intuitively know. That is not real life though.
Good lovers are good communicators.
However, the vast majority of American women are happy with one or two. Often the second or third orgasm is much weaker than the first. If a spouse loses interest, it could be related to many different things. Maybe they feel too fat, too stressed, etc. Maybe they are carrying resentment towards their spouse.