If you have two identical items in your inventory, you can refer to them seperately by adding a number, eg. 'look at dagger 1', 'look at dagger 2'. The same goes for selling and other associated item references. Be aware that once an item temporarily gets relocated it may change number when returning in your carried inventory. So if you want to make sure you do not sell the wrong item, you can choose to keep one of both items or remove it from your carried inventory temporarily by dropping it or placing it in a container.
Have a read of help parser for more information about differentiating between objects.
m.ariaans, t.roberts |