How can I see if my XAMPP is running 32 bit or 64 bit?

You can use this command on your cmd - D:\InstalledSoftware\xampp\apache\bin\httpd -v Find your xampp folder then type this- \apache\bin\httpd -v

For More Details- https://superuser.com/questions/791887/apache-version-in-xampp/1091133

If you're running windows, XAMPP is running a 32bit version of php, no matter of the installer's architecture.

UPDATE 10/23/2019 It would appear that since the latest build (Sep 24 2019) Xampp now serves x64 by default and not x32

You can check your version by running php -v and reading the build date & architecture

May be is a trick, but it lets you know if your are running PHP on 32Bits or 64Bits, you have just to print the PHP_INT_MAX constant.
This is a related answer https://stackoverflow.com/a/27949902/4098311