Agnoric Rune is chaired by going to patrol on the Dreadnaut and looking for those taken portals. Once going near them and activating them it should spawn a group of three taken four times. The fourth time, a tier two (yellow named) enemy will spawn. You must get the kill to get the charge. The rules to getting a charge on your rune is once every game reset a day. This typically means when bounties are refreshed. If someone has a charged rune, you can piggy back with them to charge your rune, or complete that mission by opening the treasure box when the other party received it. I hope this information helps, and best of luck guardians.