is it a good excersize for forearms
to rest your arms on legs then grab a dumb bell or long bar
and keep your arms still but move your rists up and down
can be done with under hand grip and over hand grip ?
you shouldnt really need to work forearms directly, you will get enough from basically all your other exercises. theyre pretty much genetic anyway. but if you need to do a forearm exercise try reverse grip curls or narrow grip pullups.