Q: How to pair the apple pencil with the iPad Pro?

Pull off the cap. Plug the Lightning connector into the iPad Pro's Lightning port. Done.

This Apple paper should help.

Use Apple Pencil with iPad Pro - Apple Support

Do you have Bluetooth turned on in the Control Center ?

Try doing a forced restart first, you can see how in this link below. All you do is hold the side sleep/wake button and the home button until the apple logo pops up on the iPad showing that it is restarting.

Restart your iPhone, iPad, or iPod touch - Apple Support

Then try and follow these steps once again!

Use Apple Pencil with iPad Pro - Apple Support

Also, make sure the Apple Pencil Tip is screwed on correctly.

This could be an issue as well:

• "If you turn off Bluetooth—for example, if you turn on airplane mode—you'll need to turn on Bluetooth and pair your Apple Pencil again."

Go to settings> Bluetooth and turn it on and off. Attach the pencil to the Pro again. If you don't get a pair button go to Bluetooth in settings again and see if the Pencil is listed.

If it says it connected give it a try to see if it works.