Who sells jewelry?
Solution 1:
Diablo III has a handful of merchants, but for the most part, they are named for your convenience. Specifically, only merchants known as, "... the Fence" will sell you "Trinkets", which include both amulets and rings. They will show up on your minimap as "Fence".
Act I: Radek the Fence
Radek the Fence is in the Nortwest part of Tristram, on your way towards the Northwest gate.
Act II: Silmak the Fence
Silmak is also chilling in the Northwestern part of the town, though in his case, he's overlooking the city, a little east of the healer.
Act III & IV: Litton the Fence
Litton is hiding in the southmost part of the Worldstone Keep area, where he will sell you the belongings of dead soldiers.
Solution 2:
Any vendor that is a Fence (seller of stolen goods) will sell jewelry.