At what level of photography do I need to be to take a workshop?
Good question. Most people who take a workshop already have a grasp of photography basics.
You should understand what aperture and shutter speeds are and also understand the relationship between aperture, shutter speed, and ISO in making an exposure and you should know how to change these settings on your camera.
You should understand the term "stop" as it pertains to photography.
If you're unsure how aperture and depth of field relate to each other, don't worry. I can help you sort that out.
You should be generally familiar with your camera controls. Like how to place your camera in the Manual exposure mode or how to change metering patterns. You should know how to view the histogram on the back of your camera and how to change the white balance. If your camera has a mirror lock-up function or self-timer you should know how these work. You should know how to format your memory card. All this can be found in your camera's manual.