An Apple Pencil has not outward method by which to verify the state of its battery. Unless that Pencil successfully pairs with your iPad - and the battery state verified from iPad settings or the battery widget - you cannot be certain that the Pencil has successfully charged.
When paired, you can see the state of the Pencil's battery charge in iPad settings:
Settings > Apple Pencil

You can also install a Battery Widget on any of your Home Screens - or the slide-over Today view.
Add, edit, and remove widgets on iPad - Apple Support
If the Pencil won't pair with your own iPad, try pairing with a different compatible iPad. If you don't have immediate access to another iPad, consider visiting a local Apple retailer that has demo' units on display - and try pairing the Pencil with a demo iPad. If the Pencil still fails to pair, it is very likely that the Pencil or its tiny internal battery has failed. If the Pencil does pair, then the problem lies with your iPad.
You should note that the second generation Apple Pencil is only compatible with these models of iPad:
- iPad mini (6th generation)
- iPad Air (4th or 5th generation)
- iPad Pro 12.9-inch (3rd, 4th, 5th, or 6th generation)
- iPad Pro 11-inch (1st, 2nd, 3rd, or 4th generation)
These support pages may be helpful with pairing and use of the Pencil with your iPad:
Connect Apple Pencil with your iPad - Apple Support
Charge your Apple Pencil and check the battery - Apple Support
If you continue to experience difficulties, here is one of the better troubleshooting guides:
https://appletoolbox.com/apple-pencil-not-working-heres-our-troubleshooting-guide/
Be aware that if your Pencil has been set-aside for an extended period, unused and uncharged, the Pencil battery may have been damaged through deep discharge. In common with all Li-ion batteries, they must always have some level of 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.
Gentle warming of the Pencil (such as placing on a hot water radiator), prior to attempting charging of the Pencil, can sometimes resurrect a dead Pencil battery.