Any laptop will do but a netbook will be more convenient to cart around. Kali Linux works on anything, even on an Android mobile phone.
Please don't use the word "hack" in the same sentence with Pen-Testing. One is illegal and anti-social and the other can be a very worthwhile and well-paid living. Make sure you get an official corporation Purchase Order in your hands before taking any action.
Take the course to learn Pen-testing properly but make your decision first which of those you want to do.
You'll get no help here if you choose to go down the "h" route.