I can trigger one Forbidden Knowledge on Mythos phase with Agnes, deal 1 damage, then trigger the second in enemy phase, dealing 1 damage, then in upkeep( after they ready) for a third ? I may use Mind Wape on Harbringer of Valusia, kill him in that round and remove it from campaign without taking 5 vengeance ?

No, she can use the first two, but not the upkeep one. The player window that would allow you to trigger Forbidden Knowledge during the upkeep phase happens before exhausted cards are readied, so you'd have to wait until the next round.

Harbinger is elite, so Mind Wipe won't work on it. Otherwise, you would be correct - Mind Wipe removes Victory and Vengeance from non-elite enemies. In a horrific twist, if Mind Wipe did effect the Harbinger, slaying it would instead discard it into the encounter discard pile... yay?

Thank you. Did not see the Elite on harbringer.