You have to go to Xer's hideout to get the training talk. If he's not home, try going the next day.
It's still not working if you go to his hideout BUT I triggered it when Xeroth was asleep, Rhot will be waiting for him then you have the talk option "Training" with Xeroth at his hideout after that I could finish the quest: "Sleeping Issues". The problem with this event is that he needs to oversleep and I think is badly implemented because when I was recreating* step by step what I previously did to trigger it Xeroth was awake and was with Rhot, maybe it's random I don't know.
*I was sleeping to 9:00 am on Saturday and was visiting Rhot who was waiting for Xeroth. I was loading previous saves before for the first time event: "Training" with Xeroth and Rhot will trigger, but it happened only once for me :/