put a sketch with a line or curve where you want the data then use the 2D tool in the results section to plot the data.
Aside from the XY data point extracted on a sketch, which is going to be very painful to have tens of sketches on that area, I would like to suggest a bit more convenient way which has its own pros and cons.
Use point parameter. Herein, you may initially find it useless as you has to have a valid entity (surface) at the location of interest. In that case, you can define a dummy component into your duct and exclude it from the flow sim; thereafter, use it as reference face in point parameter and extract all info on that face in terms of data point. You have few options in there, explore and see which would be most appropriate for your needs.