NPCs do not have inventory other than the attachments they are wearing as defined in their appearance cards. There is no OSSL code which will detect inventory changes on NPCs which would allow the triggering of a 'give' event.
A prim can be scripted to accept content from a user much like the inworld mailboxes of old in SL. On inventory change of the mailbox, it can be scripted to say 'thank you' or give the user inventory you have stored in the contents of the prim.
ActiveNPC does allow your NPCs to give items from the controller contents using actions you define in the ..extension script. This can be handy if you have bartenders or cocktail waitresses. Normally, the NPC would walk up to the guest and ask them to make a CHOICE from the available items they have to give. The active NPC page has more details on setting that up.
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