You need to talk to the praying old lady in Ashina Castle for the speech option to appear

you are too late to do this (got too far in the game), you can try and dive for it in Mibu Village or suck it up and go for thjis ending next playthrough like I did

Haha suck it up & wait for ng+? Why? Up until you beat divine dragon you can still do the set up for all 3 endings Post geni dive down after corrupted monk and get the tome Get the rice/give to kuro/serpent visceras/frozen tears And eavesdrop/Emma/old grave/dilap/bell/beat owl rematch You can do both, so once you beat divine and come back for the final fights you can just give the item for the ending you want

must go before winning the Genichiro

ok so i figured it out. it's actually at the bottom of the pond at the Temple Grounds idol at Senpou. You need the ability to swim to get it.

it seems to be Or. The Monk is only there if you didn't talk to Kuro after killing Genichiro (though I really want to confirm this myself, I can at least 100% confirm the monk is there if you kill Genichiro but did NOT talk to Kuro). If the monk's already gone, then you get a second chance at finding the item in the pool, but at some point in the game when you progress the game to a certain point, it won't be there anymore either.

Seems this is correct, I also killed Genichiro and found no monk here for me just the bell.

This is not true. You can kill Genichiro, but it seems you cannot talk to Kuro AFTER you killed Genichiro. I just killed Genichiro, did not talk to Kuro, made the run to the temple to verify the monk is there to give me the item, and the monk was indeed there and gave me the item.

also it didnt reappear in the lake, or go to the offering box

You have to get to the main hall of senpou temple before killing genichiro. If you've already done that, you can find it in the pond below the temple grounds waypoint

You first need to talk to the old woman on the bridge near the Ashina Castle Idol. Only then will the speech option appear. Hope this helps!