Here is one of the better troubleshooting guides for the Apple Pencil that may be helpful in working through common issues. This is applicable to all models of iPad and Apple Pencil:
https://appletoolbox.com/apple-pencil-not-working-heres-our-troubleshooting-guide/
As described, your Apple Pencil may be displaying symptoms of a failing or dead battery - that will not accept or hold any charge.
The tiny internal Li-ion battery is susceptible to permanent/irreversible damage through being left discharged for long periods. Even some “new” pencils can exhibit signs of failure out-of-the-box if they are “old stock”. It is essential that if you have an Apple Pencil that you charge it regularly - whether used or not - so as to protect the battery from deep-discharge. Do not allow a pencil to remain in low-charge state for any period of time - as the internal battery will fail, rendering the Pencil useless. Setting aside an unused Pencil, for extended periods, is a recipe for premature death of the Pencil battery.
If the Pencil Battery has failed, the only remedy is to replace the Pencil. If the battery has failed and your pencil is within its one-year warranty, you should look to having it replaced by your retailer or at an Apple Store.
