External keyboards do not have the Fn button because that feature is a laptop-specific characteristic. The Fn buttons are coded into the laptop to control specific features of the device. Thus no generically-supplied external keyboard can be expected to be able to replicate the functions. You are best to purchase a new keyboard for the laptop. They are usually not too expensive and can often be replaced rather easily. Some laptops are more difficult than others, but there are many videos on YouTube that show how to do these.
In fact, here is a link to a YouTube video showing how easy it is to remove your keyboard. They don't get much easier than yours....
Asus X5DAF X5DC X5DIE X5DIJ X5EA X5MJ keyboard replacement
If you Google "ASUS X5DC Keyboard, you'll find you can get a replacement keyboard for 20-25 USD.
×