I am willing to add another tone potentiometer to my guitar and I wanted to know what is the best way to add a hole in the pickguard for the new pot.
Is there a dedicated tool for this task? What is the best and safest way to achieve this?
Your simplest bet is just to use a drill bit suitable for plastics (assuming it is a plastic pick guard)
I would probably use a small bit first, then one with the correct diameter for your pot, or better yet, something like this, which gives you the best of both worlds.
This is the Armeg WWB10.0T Wood Beaver Drill 10mm