That's a good question, but unfortunately the tools for doing that are not good.
You can use lmutil lmstat https://www.mathworks.com/help/install/ug/network-license-manager-tools.html and read off the "total of <N> licenses available" and then parse the output after that to see how many are in use.
However this is probably not going to go well if there are group licenses: if you are part of a Group then you care about what is available for the Group, not everything the license manager handles. Likewise if the licenses are restricted in other ways such as reserved by IP address.
