This video shows a hammer curl. It is the best of the forearm exercises for developing the brachioradialis. The still photo shows the brachioradialis with a light pink color highlight for those unfamiliar with the muscle’s location. The muscle becomes very prominent in the video. Other exercises that flex the elbow stimulate this muscle, but none as directly.
The exercise is being done with a thick handled dumbbell to develop grip at the same time as developing brachioradialis. This may be a good way to start out, because less weight can be used than with a standard handle. After a while, you can switch to a standard handle to use more weight for the brachioradialis, and do a separate exercise for grip.
The video shows using a full range of motion for this forearm exercise. After the elbow is flexed to a right angle (parallel to the floor), the biceps becomes the main muscle stimulated. The brachioradialis is static. An increased intensity technique, after some experience with the exercise, is to do the hammer curl only slightly past a right angle. More weight can be used, and less rest provided to the brachioradialis during the set.