Trinket from Sha'ira

If you take on the quest Citadel: Asari Consort on the Citadel, you'll likely receive a trinket from Sha'ira (the Asari consort) at the end of the quest. She'll explain that she has no idea what its purpose is, but that she senses you may need it.

The trinket's purpose is never made obvious — you sort of need to stumble upon its use. In the Hecules system of the Attican Beta cluster, there is a planet called Eletania. (This planet is also where you complete the UNC: Lost Module assignment — the "monkey" quest.) When you land on this planet, you'll see an anomaly marker on the map.

There, you'll find some Prothean ruins, with a strange metallic sphere. If you examine it, you'll be prompted to insert the trinket you received from Sha'ira. When you do, the sphere will rise up. Check it again and you'll discover the information held within.