There are multiple ways to find out:

• On Sprintr, you can check which Mendix versions are currently deployed to your environments by checking the details page for that environment:

• If you want to know the Mendix version of a specific branch without downloading it, you can check the “team server” page in Sprintr and find the latest commit:

• If you have a branch already downloaded, simply open the project folder and double-click the project file. It will try to open the project in the correct Mendix version. If it's not installed, you will get a notification saying which version it is and give you a choice to open it with a different Studio Pro version.