I have a E3 Cycling bike computer that does not work. It is not picking up any speed at all. How close does that magnet on the spoke have to be to the fork thing? Maybe I should get a wireless one?

On my planet bike computers, the magnet works great within a millimeter or two. I normally set the magnet, and then adjust the wired receiver into the sweet spot.

Yup, pretty darned close--nearly touching.

The other thing to consider is where inside the sensor housing the actual sensor is. On the cyclometers I use, while the housing is an inch or more long, the the actual sensor itself is in one end. Adjusting the magnet to the middle of the sensor results in no reading.