It is not really needed if an iPad Pro is using a smart cover to protect the screen.
A screen protector is really NOT a '“need” per se, but more or less an optional and individual decision to purchase and use.
If you plan on using an Apple Pencil or some other type of capacitive or Bluetooth stylii, you maybe better off without a screen protector as screen sensitivity may diminish slightly with some compatible apps.
If you plan to try and use a “matte finish” screen protector, these are great for writing or drawing with an Apple Pencil OR other, third party stylii, and fingerprints are kept to a minimum, BUT the biggest drawback to using matte finish screen protectors is that it will impact/degrade the quality and resolution your large screen iPad Pro’s screen noticeably.
I have been using various iPad models for nearly 8 years, and I have never felt the need or want of using any screen protectors on them.
The choice to do so is a purely individual preference.
Good Luck to You!