Jez Blanchard | Jackson Kayak - Basically it is a cartwheel in one direction into a cartwheel in the other direction.

Here is the ICF definition of what a Splitwheel is:

Two consecutive ends, with a change of direction in between each and both ends at a vertical angle between 45° and 100°. The value of a splitwheel is 40 points.

You should be proficient at your cartwheels in both directions, practice your cartwheels before your try this move. Start off practicing the splitwheel on the flat, no need to try to go very vertical, instead just try to complete the move with a small amount of edge. Complete a cartwheel in one direction and transition over to your other edge. Open up the face of your blade to allow your push stroke to be changed into a pull stroke.

Common mistakes are edging your boat too much which will mean you will fall on your head, to prevent this just don't edge your boat so much. The video shows it all, check it out and get proficient and your splits.