Where you would normally turn in your Writs in your factions capital city (wayrest, elden root or mournhold)
I turn in my writs at Craglorn..
You are referring to regular wits. When you turn those in you get a small chance to receive a matter writ in the container. Choose goodbye when it prompts the dialog so that you can review the sealed writ.
If you are able and willing to craft it then accept the quest. If not, sell or trade it.
Yes, that dude in Mournhold. Unless there is a temporary bad glitch, you can always see the white or black quest markers on the map for an active quest or get more direction/information from the journal section.