i need to know where the staff of earth is

I'm not sure if you mean Staff of Earth or staff of woodlands, because I get the two mixed up, but there is a staff that can summon a shambling mound, which would sound like the staff your looking for; Its in The Elven City around the last chapter, you get it for saving the city, and it is a gift from the Elf God.

That would be the staff of woodlands, the staff of earth is in drow city IIRC.

The staff of earth can be bought in Ust Nastha (the drow city, not sure about spelling).