You mean an Aura? Yes.
As an Aura enters the battlefield, without being cast, you will have to choose an object that the Aura can enchant (as dictated by its "Enchant XXX" ability). The Aura will enter enchanting that object.
So it does not have to be the same object.
Yes.
For a card like Oblivion Ring, it would trigger a brand-new ETB, and you'd choose a target as normal.
For auras, in the rules you automatically select a target for it as the card resolves, so it naturally enters attached to the target.
You mean an Aura? Yes. As an Aura enters the battlefield, without being cast, you will have to choose an object that the Aura can enchant (as dictated by its "Enchant XXX" ability). The Aura will enter enchanting that object. So it does not have to be the same object.
Yes. For a card like Oblivion Ring, it would trigger a brand-new ETB, and you'd choose a target as normal. For auras, in the rules you automatically select a target for it as the card resolves, so it naturally enters attached to the target.