How do I make an item fall out when I click on a mob with scissors?

you can go to the trigger page of your custom mob, and select the trigger "when entity is rightclicked". in that procedure, you make an if-block to check, IF: the source entity (the clicking player) is using scissors. THEN: Spawn Enity: Cow at xyz of the event target entity, with yaw and pitch of event target entity, spawn dropped item at xyz of event target entity then despawn event target entity.

the spawn entity and dropped item blocks are under worldprocedures:action, getting yaw and pitch are under entityprocedures:data.