How long does it take to charge an Apple Pencil?

The iPad will show the charge of a paired Apple Pencil in the Battery Widget in the Today View of Notification Center:

Use Apple Pencil with iPad Pro and iPad (6th generation) - Apple Support

You can add the Widget by following the steps here: Use widgets on your iPhone, iPad, and iPod touch - Apple Support

As to charging time, if connected to an iPhone or iPad charger is should be fully charged in around 10 minutes.

If charging through the lightning port of an iPad or iPhone it may take longer to charge to 100%.

Apple Pencil fast charges in 15 secs to you 30 minutes of use.

If you wish to fully 100% charge your Apple Pencil, it will charge at a slower, more steady rate of charge and charges to 100% in approx. 20 to 30 minutes, or so.

To monitor the Apple Pencil battery, add the Apple Pencil Battery widget to your iPad’s notifications panel.

Uh,

No.

The Apple Pencil if near depleted, will fast charge for 15 seconds and give you a quick 30 minutes of power.

If you need to fully charge an Apple Pencil to 100%, the Pencil will charge at a slower, more even rate of charge.

It should take approx. 20-30 minutes, or so, for the Apple Pencil to charge to a full 100%.