If you install just the client tools on your workstation, you will get the SmartObject Service Tester exe as well. You can also just copy the SmartObject Service Tester exe from the server to your workstation, but I believe you will need some dependency dll's as well so I recommend the client tools installation.
Copying the entire Bin folder where the Smart Object Service Tester resides in should allow the tester to work. You do not have to install the entire client tool though if you only need the tester tool.
Please note that I have seen a number of complaints regarding the tester, as it can grant you access to all service instances and SmartObjects on all your K2 environments. If you did not configure permissions for users who are allowed to access certain categories, all users will be able to access the SmartObejcts in those categories using the SmartObject Service Tester. This means anyone can just go in and remove the SmartObjects from your environment.
My recommendation is to not distribute the tester, and just keep it to yourself if you are using it for testing or development purposes.