This app was mentioned in 3 comments, with an average of 2.67 upvotes
and here are others that help, I need CLI practice so a mobile alternative with CISCO is awesome here is more on that
https://play.google.com/store/apps/details?id=com.rtheory.practicesubnetting&hl=en
This is a good one because you can choose which aspects of subnetting to guess/study.