Thanks for contacting us with your question!
It depends on what you need those coordinates for. The easiest way is to show how to draw rectangles on both the corners of the chart. I did that using Highcharts.SVGRenderer
The first argument when drawing the rectangle is the x coordinate and the second one is y. If you want to place something in the top right corner, check the coordinates of the first rect drawn, basically, it's based on the chart.chartWidth and for the bottom left corner we need chart.chartHeight as in the second rectangle.
Let me know if that was what you were looking for!