Can Dragon Slayers teach Dragon Slayer Magic? Can Dragon Slayers teach other people Dragon Slayer Magic just like how the Dragons taught them?
According to the Wiki, Dragon Slayer Magic is a form of lost magic. We know that Ultear was able to learn a form of lost magic called "Arc of Time" from Hades.

However, we know that there are currently two ways you can obtain Dragon Slayer Magic:


Learn it from an actual Dragon.
Implement a Dragon Lacrima into your body.


Therefore, I would say yes, this might be a third way to teach someone Dragon Slayer Magic.