1) According to Ay Sistani the najasat domino effect ends at 2 example if a dog touched a wet shoe and new wetness came to the shoe and it touched the ground and new wetness came to the ground and if I touched the ground I would not get najis

-Does it need to be new wetness what if it’s the same wetness from the initial najasat that stayed there through all the 3 items?

-What if you have doubt if it’s new wetness or wetness from the previous najasat?

-Example there was a dog on snow or rain and the wetness might be the same and you stepped with your shoes and then stepped on the floor etc?

2) Do you need to recite sajdah sahv if you repeat dhikr in jamaat or regular Salah or if you have doubt or if your body moved and you repeated it..

3) Sometimes I get doubt and go back to redo the dhikr is that ok? So I need sajdah sahv example in tashahud and salam or the 2 suras I think about it the doubt and continue but then come back to recite

1- Yes. It has to be new wetness in all cases.
2- No.
9- No need for sojood sahw.