can i use ipencil to paint on photos on ipadpro?

If you have an App that supports this, sure.

A Google search produced this:

http://www.creativebloq.com/software/ipad-apps-make-most-apple-pencil-121518448

and quite a few more:

https://www.google.com/search?q=apps+for+apple+pencil&ie=utf-8&oe=utf-8

There are many Apps in the store that support it. Try looking for some drawing Apps in the store or on Google, a quick search produced this one:

Link to App:

https://itunes.apple.com/en/app/you-doodle-draw-on-photos/id517871755?mt=8

Link to Google Results:

http://lmgtfy.com/?q=Apple+Pencil+Draw+on+Photos