How to connect Apple pencil (1st Gen) to ipad pro (2nd Gen)

Here is the definitive compatibility list for Apple Pencil and iPad:

Apple Pencil (2nd generation)

You can use Apple Pencil (2nd generation) with these iPad models: 

• iPad Air (4th generation)
• iPad Pro 12.9-inch (3rd generation) and later
• iPad Pro 11-inch (1st generation) and later

Apple Pencil (1st generation)

You can use Apple Pencil (1st generation) with these iPad models:

• iPad (8th generation)
• iPad mini (5th generation)
• iPad (7th generation)
• iPad (6th generation)
• iPad Air (3rd generation)
• iPad Pro 12.9-inch (1st or 2nd generation)
• iPad Pro 10.5-inch
• iPad Pro 9.7-inch

Not sure which iPad you have? Identify your iPad model.

To summarise the above compatibility list:

• if the iPad has a USB-C port, the iPad is only compatible with the second generation Apple Pencil.
• if the iPad has a Lightning port and has support for the Apple Pencil, it will only be compatible with a first generation Pencil.

The two different versions of Apple Pencil use a completely different pairing/charging interface. The Pencil versions are not interchangeable.

Assuming that you have an iPad that is compatible with the version of Apple Pencil that you have:

Connect Apple Pencil with your iPad - Apple Support

What size? The 12.9" iPad Pro had two generations before the 11" came out.

The 12.9" iPad Pro 1st or 2nd gen works with the 1st gen Pencil. Plug the Pencil into the iPad to pair them and charge the iPad.

The 11" iPad Pro 1st or 2nd gen works with the 2nd gen Pencil. Adhere the Pencil to the top edge of the iPad magnetically.