Creating a item that can store unique data of entities

Hello all,

sorry if I am at the wrong place in the forum with my problem or if my questione isn't formed correctly.

I tried to create an item that, when right clicked on an entity and/or player, stores their "unique tag" so that the item later can be used in rituals to, for example, curse this entity or player.

My (very wrong) first attempt: https://imgur.com/I6o5LLF

My (also very wrong) second attempt: https://imgur.com/eXjNJvg

I also linked this procedure to the item trigger "When right-clicked (entitiy pos.)"

I searched the internet for days for answers and watched the online tutorials that cover NBT but i just don't seem to be able to wrap my head around it.

Hopefully you may be able to help me.

Thank you very much in advance <3