I had mine installed on the left handlebar, the standard location for the J&M CB (and the same unit they make for resale by BMW).
I really prefer the BMW-branded version of this unit because it includes a thumb-operated push-to-talk (PTT) button which is positioned exactly where it should be for easy/intuitive operation. The J&M radio has a PTT button built into the body of the radio, which requires removing your left hand from the grip to operate it.
(see 2 attached photos for my setup)
Some people mount the CB radio on a tank bag - again, not as convenient to use, but then you can take the radio with you at night, when you go into a hotel, etc. Everything is in or on the tankbag, and that has its attraction. Here is a photo of how RKA suggests installing it. Notice the PTT button on the bottom left of the CB radio. You operate it by pressing down with a finger.