Eh, logically speaking if hitting things works - and we know it does, otherwise the weapon's effect would not trigger in battle - then it stands to reason that touching should work as well. The former is short contact, whereas the latter would be prolonged contact. I somehow doubt that violence inherent in the first act is the trigger here.
Things seem super unclear, but Arivia seemed to confirm that the blade was at Karaz's feet. So I don't need to make a dex roll. I just need to touch it.