The Barbell Wrist Curl is a good exercise for building grip and forearm strength.
Barbell Wrist Curl Works
HOW TO DO BARBELL WRIST CURLS
Grasp the barbell with an underhand and narrow grip, sit on bench and place forearms on bench.
Doing the Exercise
Gently lower the barbell towards the ground and extend the wrist. Pause, and curl the barbell back up.
Lower and repeat
Keep your arms flat on the bench
Using too much weight.
Lifting your forearms from the bench