According to the user's guide, the CTK-519 has MIDI In/Out ports, so you'll need to use a MIDI-to-USB interface (which I gather you've already bought), but you might not need a driver for it. If you do need a driver, it should be the driver that's for the interface itself, not a driver for the CTK-519.
Be warned that a lot of the cheap MIDI-to-USB interfaces are unreliable as far as quality and dependability, so if the interface you bought doesn't seem to work, you might need to buy a different one that isn't as cheap.
As for drivers, they are specific to a particular operating system, so you'll want to look for the correct driver for whichever operating system you're on. Also, if the company that makes the MIDI-to-USB interface doesn't have a web site where you can search for product information and look for drivers, often that can be a warning sign that the interface is of unreliable quality, because any company that makes quality products is likely to have a web site for its products.
If you can find a driver for other operating systems, but not for your operating system, then it might be that your operating system doesn't need a special driver. For instance, if you're using a Mac or an iOS device, you most likely won't need a special driver for the interface, because it should work with the standard drivers that are part of the operating system.
What is the name of the interface you bought? What kind of computer and operating system are you trying to use the CTK-519 with?
EDIT: The title of your thread mentions "MacOS/Windows," so it isn't clear whether you've got a Mac or Windows computer.