Combine coriander, fennel seeds, brown sugar, paprika, garlic powder, onion powder, and mustard seed in a small bowl.
Place brisket in a glass baking dish and rub spice mixture all over. Cover with plastic wrap and place in the refrigerator for 2 to 3 days.
Soak wood chips in water for at least 1 hour.
Preheat a smoker to 240 degrees F (116 degrees C) according to manufacturer's instructions. Maintain temperature for 15 to 20 minutes.
Drain wood chips and place on coals. Place a water pan on the smoker and add water to the depth of the fill line. Place brisket on the lower cooking grate and cover with the smoker lid. Smoke for 2 hours.
Pull brisket from the smoker and wrap tightly in foil. Return to the smoker until an instant-read thermometer inserted into the thickest part registers at least 190 to 200 degrees F (88 to 93 degrees C), about 3 hours.
Remove brisket from the smoker and let rest for 40 minutes. Slice corned beef against the grain.