If you’ve not already done so, ensure that you have updated your iPad to iPadOS 13.6. This update includes patches for a number of functional issues, including one affecting pairing and operation of Apple Pencil with some models of iPad.
Your Apple Pencil may displaying symptoms of a dead battery - that will not accept or hold any charge.
Assuming that you do not have any other iPad charging issues - and that the Lightning Port of your iPad is free from debris - whilst the Pencil is plugged-in to the Lightning Port of your iPad, verify that the Pencil is recognised:
Settings > General > About
Scroll to the bottom of the page - and you should find two identical entries for the Pencil (one each for the physical and Bluetooth connections). If both are present, the electronics of your Pencil are likely to be good; otherwise the pencil may have a fault, or there is a pairing issue.
Whilst the Pencil is connected to the iPad, using the Battery Widget, verify the battery charge state whilst connected to the iPad. Allow to charge to 100%. When 100% charge is seen, disconnect the Pencil from the iPad; if the charge level drops significantly, or the Pencil battery status disappears from the Battery Widget within a few seconds, battery failure is likely.
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.
If the Pencil Battery has failed, the only remedy is to replace the Pencil. If purchased directly from Apple and the Pencil battery fails within its one-year warranty, you should look to having it replaced. Apple will usually replace an otherwise undamaged Pencil within its warranty period without quibble.
You may also find this troubleshooting guide to be helpful with general issues affecting the Apple Pencil:
https://appletoolbox.com/apple-pencil-not-working-heres-our-troubleshooting-guide/
I hope this information proves to be helpful in both diagnosing and resolving the problem.