Apple Pencil v2 Charging Post 100%

Wouldn't keeping it on wireless charge nonstop for hours-days without use continually damage the battery of the pencil?

No.

Isn't there any way for the pencil to detect when it's fully charged and for it to stop (shouldn't it be doing that)? Or is it doing that and just not showing it on the battery display widget?

It does do exactly that. But the indicator on the battery icon in the widget does not change to show this.

The Apple Pencil cannot be overcharged. It will charge to 100%, and stop. then wait until its charge is I think around 95% and charge again.

There is no issue with leaving it attached to the iPad continuously other than it will drain the iPad's battery eventually if the iPad is not plugged into power.

Neither the Pencil's not the iPad's battery will be damaged by this however.

Apple has never offered any lithium battery powered device that can be over-charged. They always use major brand batteries built to international SMART battery standards, and those standards require over-charge protection be built into the devices own charging controller - whether that device is a pencil, a laptop, a tablet, a toothbrush, a car or whatever.

Any lithium battery powered device, of any kind, using batteries built to international battery industry standards cannot be over charged. That’s the whole point of having globally recognized and observed industry standards for lithium batteries and lithium battery powered devices.

Only the cheap products built without observance to those standards are an issue - some cheap spontaneously combusting “hover board” toys of recent past come to mind.

You will not hurt your pencil by leaving it on charge even after it has reached 100%.