When you play Talented Arcanist next spell you play has Spell Damage +2. So, if my next spell is Cram Session, it should draw 2 extra cards. In my case it didn't. You can see it says draw *6* cards and I only drew 4.
Talented Arcanist is completely bugged. Days ago, while doing an arena run, I remember playing a spell that deals damage to multiple targets (not at the same time, but one by one) and only the first minion received the damage improved by 2. I'm pretty sure that's not how it should work.