@I'm assuming this is for your ToK essay, in that case robust is how you define it as long as you are able to back it up with evidence. For me I defined robust knowledge as something that has evidence and is not able to be questioned. As a general definition robust is something that can withstand forces upon it well. You only need to cite something when it is not yours, such as another's idea or quote. For the ToK essay, you don't have to quote anything as it is an argument of your own, but it may help your case to cite a historical refrence, depending on which AoKs you use. Hope this helped.