Personally I took Amaram’s reasoning that he couldn’t just ask Kaladin for the Shards because obviously he would be convinced by everyone else to ask for them back to be pretty clearly in bad faith.
I'm iffy on this theory because it relies on specific wording in a boon/bane when that seems to contradict how the Nightwatcher was told to work in WoK: that it wasn't a matter of wording your request correctly, but she just gives you what she thinks you deserve.
Painrials only numb pain (they're a dminishing fabrial), and it doesn't make sense for something that's designed for physical pain to help with emotional pain , or the lack thereof, in this case.
I don't think so, there's no opportunity for him to have found out, and I think it would've been mentioned if they released the news that the Assassin in White had been killed.