how can i prove that corin is innocent...talked with sandra ullman so far but still nothing..no clues from there

First, find the petrified paladin in Swartzwald. Next to him you'll find a golden earring. Take it and then talk to the beggar in the northeast part of the city, next to the cathedral. He'll tell you about Sandra Ullman and then you need to confront her about the earring.

and where is the petrified paladin in schwartzwald couldnt find him

nvm,i found it..