I’m noticing a lot of women started wearing a skirt with leggings underneath. Sometimes ankles are exposed and sometimes not. Is there an issue with this practice?
Wearing a skirt with leggings can have halachic issues. Even if the skirt has leggings the skirt has to be the correct length and cover the bottom of the knee in all positions. Aside from that, the ankles should be covered, however that can be taken care of by wearing socks on top or underneath the leggings.
In truth though, even if the leggings are technically tznius, there is another issue here. If the reason the person is wearing them (even if it is only the reason deep down inside) is in order to give off an appearance as if she is wearing pants, (even if it has a skirt on top of it) which are meant for men to wear and not women. This is more of a hashkafa issue, that women should dress like women and stay away from styles that are pushing the boundaries of halacha.