Yu-Gi-Oh! » Rulings Q&A

Can you use showdown of the secret sense scroll techniques to negate an hand trap like effect veiler, drill and lock, ash, winter cherries Ect?
hand traps discard themselves on activation meaning their in the graveyard so it the timing correct to activate showdown of the secret sense scroll techniques to negate them even if their wasn't a 2nd copy of them in the graveyard prior to this?

Yes, you can chain Showdown of the Secret Sense Scroll Techniques to the activation of a hand trap that discards/sends itself to the GY as cost, as it is already in the GY by the time the opposing player has the chance to respond. This makes Showdown of the Secret Sense Scroll Techniques legal to activate, even when there is only a copy of the associated hand trap in the GY.

You can legally activate Showdown. Reason being is that Ash blossom discards itself as a cost. So it is now in the grave before it can resolve. Showdown only needs a card with the same name as the activated card to be in the graveyard. So after the cost of ash blossom, since the activation requirements for Showdown are now met, you can chain it directly to ash blossom and negate the effect.