There are also Kamasylvia Mountain Goats and Kamasylvia Young Mountain Goats around it to S rank knowledge on.
Doubling your chance can be done with fluid collection, Butchering or Tanning.... and yeah it's a lot of sitting around.
There is another Rock Rhino imaged below:
I can confirm XIIOIV's picture, that Rhino is still there. Approach from the northern road (the one to Valtarra), don't forget your Weenie Elixir and whatever you have and your life skill tool to have a second chance on the knowledge.