If you mean you want to add nodes in between the existing nodes, it would be nice if like in some other applications there was an add node (point) which is customary for those applications to split the distance between the node clicked on and the next node.

But you can use the line tool to draw a vertical and a horizontal line, both longer than the circle. Group them. Rotate 45 degrees. Then select the circle, select the shape editor, click on the circle where the lines cross.