1) This quest is a sequel to Art of Persuasion. You must be level 41 and have "Loraine's Certificate" in your quest inventory. After the last quest you should already be standing in front of Researcher Lorain.
2) Lorain has found out that the metal plate you discovered in the Cruma Tower is in reality a recording device used in a research laboratory of the Giants. To access the recorded data one needs a password and for that Lorain needs Maestro Nikola's help. Take the Metallograph to Nikola.
3) Maestro Nikola is still at his old position, some distance southwest of Lorain.
4) Nikola sees himself unable to decode the password, so he sends you on to Blueprint Seller Luka in the Town of Oren (what the quest screen says about "Oren Castle" is wrong). To ensure Luka's cooperation you have to bring him a fashion accessory (only one) as worn by Leto Lizardmen.
5) Leto Lizardmen can be found in the Plains of the Lizardmen, somewhat south of Oren. For this quest any of them will do: simple Leto Lizardmen (lvl 35, passive) in the southern part of the Plains, towards the river, Leto Lizardman Soldiers (lvl 37, aggressive) and Leto Lizardman Archers (lvl 36, passive) in the eastern part, towards the mountains, and the double HP Leto Lizardman Overlords (lvl 40, aggressive) in the western part, towards the road. Leto Lizardman Shamans (lvl 39, passive) and the double HP Leto Lizardman Warriors (lvl 38, passive) are all over the Plains of the Lizardmen. I got my quest item at the first kill.
There are also roaming groups of different lizardmen led by an aggressive lvl 40 Lord of the Plains. Since they don't give the Leto accessory anyway they are best avoided.
6) With your Leto Lizardman Accessory go see Blueprint Seller Luka in the Blacksmith workshop at Oren.
7) At first Luka is not very helpful, but when you show him the Lizardman Accessory he accepts the task at hand. I did this quest with a lvl 53 character, so I only got 105,083 adena. If you are between 41 and 46 you will also get 285,935 exp and 18,711 SP.
When you are level 42 you can come back to Luka and pick up the sequel to this quest - "Contract Completion".