I've never 'gotten' that line by Yoda. The first time I saw ROTS I figured that Yoda was saying that when him and Obi-Wan go back to the Temple they will duck into the archives and look at some old scrolls or something. But we see none of this, I know in the novel Vader takes some Sith holocrams (sp?) could that be the knowledge they seek? It seems that Yoda knows who killed those Padawan's (at least when he saw the saber marks he knew) but Obi needed to see it on video to belive it so that doesn't seem to be the knowledge Yoda speaks of. My other thought was the two of them would go to the archives and dig up some info. on how to transform yourself, this would be the 'ultimate knowledge' since they could continue to fight even if they are dead. I don't know that line has always bugged me.