Select the feature that you want to split and click on the scissor tool.

Please note you need to start and finish the split outside of the feature that you want to split.

Single click to start the split outside of the feature and double click to finish the split outside of the feature.

By single clicking as you draw the split you can change direction etc. then double click to finish.

Once the split tool in engaged you can hold down the shift key and then drag your cursor to draw a split shape with a double click at the end to finish.