If you are planning to start with a whole "Packer" brisket, you will have a lot of trimming to do. For a master class on this, check out Aaron Franklin at this link: https://www.youtube.com/watch?v=yaMgt1Altys. The knife he uses and we find works the best is a 6" curved boning knife. It cuts through all kinds of fat, trims silver skin, and cuts off the excess and uneven edges of the brisket.
This knife is very sharp, made from food-grade stainless steel and is dishwasher safe.