apple pencil

Your Apple Pencil is warranted against manufacturing defects for one year from its original purchase date as described here.

Apple One (1) Year Limited Warranty – Accessory - For Apple and Beats Branded Products Only.

Your Apple Pencil serial number can be found, when paired with iPad, in iPad Settings:

Settings > General > About - scroll down the list until you find the entry for the Apple Pencil, then tap.