Found in Version:
Fixed for Version:
I encountered this issue both in my big modlist and then tested it in a new game with only TR installed, so I can be sure it's not an issue at my end.
In the Guard Barracks of Firewatch Castle there is an NPC (Caccia Artoria) who greats the player with a training dialogue option.
If "trainig" is selected in the main dialogue window he talks about his sword training.
If I select "Training" in the sidebar the NPC trainer menu appears.
The "Training" option should appear as the first dialogue option in the sidebar as it is with all NPC trainers.