I completed quest saarthal when i went to College of Winterhold and got a "gauldur amulet" but i sold it and now when i have Forbidden Legend quest i can't remember where it was sold. Any one help me please @_@

Console.
Or previous save.

I'm pretty sure it's marked as quest item and not sellable. You may have not looted the body and may be confused with the Saarthal Amulet.

Ooh good point, you CAN sell the Saarthal one.

@_@, i remember i got it in the wall before i was trapped, and i must talk to oldman Toli.... and he suggest me use the amulet. @_@

That's the Saarthal Amulet, not the Gauldur one.

the gualder amulet is at the end of the quest near the orb.