how can i change plots in dots not continuous in HFSS?

That can be done in Matlab

you can very easily export your plot data in excel file and then you can use excel or any software of your choice to manipulate it. HFSS gives sufficient tools to edit the plots but I am not sure if this sort of function is available as I have never used but for sure you can export the data and then use software of your choice like Excel

Right-click the curve in HFSS.

Select Edit->Properties.

Select "Line Style" and change to "Dots".

I have one question regarding plot when we switch the line style to dot does each dot represents HFSS calculated data point?
Can I use this way to see the HFSS calculations in lets say interpolating sweep as I want to see exactly which frequency points HFSS calculated

You can also plot the individual data points.

Under Properties, check the "Show Symbol" checkbox. Then change "Symbol Frequency" to 1. Other properties will change the symbol type, color, etc.