Hold CTRL ALT F2, enter the following command in terminal.
cat /etc/os-release
This will tell you what version of OS you have, which version of Linux Zorin is coded on.
To be honest, this has been a question asked a lot on here, and there is no easy way to find this stuff out when it comes to Core, Lite etc. Its one of the things that I am hoping the Zorin team will fix in the new OS16, to give users an easy way to find that stuff out.