Not much information here as to your model of iPad Pro - or Apple Pencil (either one of which would help in inferring the other). If you not already updated to iPadOS 13.6.1 (current), you should do so.
This troubleshooting guide for the Pencil may be helpful:
https://appletoolbox.com/apple-pencil-not-working-heres-our-troubleshooting-guide/
As described, your Apple Pencil may be displaying symptoms of a 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.
For 2018 and 2020 models of iPad Pro, the Pencil should be kept docked with the iPad whenever it is not being actively used - as this will help to protect its battery from damage through deep discharge. For all other models of iPad with a Lightning port, the Pencil should be religiously charged every few days for the same reason.
If the Pencil Battery has failed, the only remedy is to replace the Pencil. If purchased directly from Apple, if the battery has failed and your pencil is within its one-year warranty, you should look to having it replaced. If the Pencil is within its one year warranty, Apple generally exchange without quibble.
I hope this information proves to be helpful in both diagnosing and resolving the problem.