Its called the humid bone forest. Its only assumed to be the slug place like how myuoboku was for frogs and the rycuhohi cave was for snakes.
I'd be guessing Naruto asks her when she learned this, she can just give a quick flashback kinda like Kabuto did in his fight with Sasuke and Itachi on how he obtained his power. Sakura's could clearly be this: "After the 5 kage summit with Tsunade awakened, I trained for the time the nations were prepping for war." Actually when this point comes around the anime, I won't mind fillers showing how she obtained it.
For anything else though, no characters on team 7 are going to die for good. Naruto and Sasuke have their fight, Sakura is too highly involved for them. The whole deal of temporary death though, people suspect its because there is a rinne tensei laying around. If the rinnegan awakens in Naruto then maybe we get something else too. I doubt Sakura learned chiyos revival technique, her death should have made knowlegde of this technique lost. Anyways I will say this, If Sakura "dies" be ready to absorb some harrassment, it will be a field day for haters but it would also be a funny pain to them all to see Sakura revived. Only thing I'm saying is, this would be a somewhat tense moment but its just due to again, theres a rinne tensi laying around, who is obito going to use it on?
I would really enjoy the "high crisis" battle in which Obito just continues with the eye of the moon plan and fully revives Madara and its up to the heroes to kill him ending the crisis for good. But there is too much left around for team 7 as a whole, they won't die peramently. I don't see Naruto dying, I don't see Sakura dying, I don't see Sasuke dying. They are the 3 next sannin, they will live till the end even if a death (temporary) comes.
Guess its best to say this to haters, if Sakura dies, she is not going to stay dead, remember Naruto and Kakashi's Talk-No-Jutsu, Obito has a rinne tensei, and Sakura is a main character, mains cannot be killed off for good unless someone has been around or set up long enough to accept the "mantle" of their role. This is near the end of the series, there is no "replacement" for Sakura, remember Naruto and Sasuke's fight for hokage later on? Well which girl espcially must be present in order for this resolve? Which girl is the mediator between Naruto and Sasuke, regardless of pairings? Without Sasuke, Naruto can't complete his goals, but this is also true with Sakura, no Sakura means Naruto cannot complete his promise to her, won't be good to complete the promise to his best friend who is killed off now? Oh yeah, SS also gets impacted by Sakura's death if it occured, but NH does too, why? Because again haters of Sakura would think that this just makes another "opening," Sakura's death would not make Naruto suddenly just switch to HInata, if anything it would make him sad and never want another girl, simply because he could not fulfill the promise of a lifetime to her, think, its the only thing she ever asked him, how would Naruto feel if he could never fulfill it to his best friend, crush, etc if she died for good? So if haters leap at this moment should it come, just remember, theres a rinne tensei lying around. Team 7 is going to be reunited in the end, Sakura is not going to just get killed for good, I mean think of it like this, Naruto has done so much for Sakura, selflessly, it would be no suprise he would defy death itself to get her back. No matter what happens, temporary death or not, Sakura is here to stay, any which way the series goes, Sakura will be living in the end.