If Aegislash with the "Durable Blade" Ability is Knocked Out by damage from my opponent's attack, do I put its underlying Doublade and/or Honedge cards into my hand or into the Discard Pile?
You put all the Pokemon in the evolution line into your hand. Any other cards attached such as Tools or Energy are discarded.
Source: Unified Minds FAQ (2019-07-19), TPCi Rules Team (2019-08-01)