How do I use/get rid of, the item that looks like a capsule with a question mark on it?

you can identify it on any merchant

ok, go to a merchant in the city and you will see the question mark down in the center of the screen that the marchant displays... click on it with the left mouse button and then in the capsule, also you can sell the purple one with conis in the right....

Go and reveal it at vendor.