Then you need to have a plot item for the embedded canvas. There are many details to learn, but as a beginner maybe start with something like the RectItem of the navigation example.

If you want to display something related to the coordinate system of your embedded plot ( f.e. a grid ) you have to overload and modify the canvasRect and canvasMap parameters in the draw methods of the plot items ( or in QwtPlot::drawItems for all items above a certain z value ). The geometry of the embedded canvas in widget coordinates ( = the paint intervals you need for the maps ) can be calculated using the original maps.

Uwe

PS: its a plot not a polt !