We suggest adding the ability to display the marker labels in the combo chart. This will expand the capabilities of the combo chart and display more measures of different types in one visual object
With the latest versions of QS, a workaround for this is to create an additional expression on top, which happens to be exactly the same, but display it as a line.
Then, on the colour options for this new expression, set the colour to be =ARGB(0,0,0,0) to make the line transparent. After that, you can enable the 'Point labels' option under Presentation tab.