It resembles a skill journal, but it's found under the sim's inventory and not under the skills. No, it doesn't appear to have levels. It's just a consolidated notebook for rocks, gems, bugs, plants and fish.
Thanks for those posting what's contained in this update. It would have taken me weeks to notice all this stuff.
I also have had a few weird routing choices. She has to leave the kitchen to go back to the fridge? Um, okay. Also, all the leftovers in the fridge spoiled in an instant. Weird, but not the end of the world.
Edit: Oh, I take that back about the end of the world. I am having problems with gardening. Nothing that's harvested goes into my sim's inventory. Eek!