I don't understand. If you've done everything in this level then you should have the 3 gems. One you get from the tanar'ri (Tahazzar), one from the demon (Ka'rashur), and one in the final room from the Cambion (Aesgareth). If you don't have all three, what did you miss, or what went wrong?
During the time I was playing SoA I start the Watcher keep and it was hard so I had only the gem of Aesgareth and I decide to stop trying to finish the Watcher Keep and continue my journey through SoA and I think I sold my gem in a store but don't witch one thinking that it was like all other jewel. So I finish SoA and I said to myself I'll come back to the keep when I'll be stronger so after I had almost finish ToB I said to myself before finishing to game I'll go back to the Keep finish it and after that finish ToB
You cannot sell them. They are plot items, have no value and are flagged as unsellable.
If you are desperate to get them, you can add them through the console. Type in the following: