Is there a console command in Skyrim Elder Scrolls V to set an undiscovered location as discovered so I can fast travel to it?
There are 2 ways to do it.
First way is to run the command
tmm 1 which enables all the map markers, which allows you to fast travel to anywhere you want.
The second way is like a workaround for this. You might not want to enable all the markers, so just teleporting there might be what you want. The command for that is
coc [the town you are teleporting to].