I would slice up the freshly smoked brisket then refrigerate it so it's all ready to go after reheating.
For small quantities of brisket (e.g. leftovers) I reheat slowly in the microwave. Place in a partially closed Ziploc bag or place meat on a plate covered with Saran Wrap; heat for 2 minutes at 20-30% power, checking and repeating until just warmed.
For a large quantity I would use the oven. Reheat slowly at 200*F in a foil-covered baking dish, foil pan, etc., spritz with a little apple juice if you feel you need to add a little moisture, and it will be great!
Regards,
Chris