Assuming that you're using Fluent, there two ways of doing it:

1. From Fluent:

File > Export > Solution Data; File Type: ASCII, and select the appropriate contour plane with the specific contour variable of interest along with the plane coordinate axes. This will export the data into a csv file which can be imported in MATLAB.

2. From CFD-Post:

File > Export > Export...; Type: Generic, and select the required surface with the variable of interest. This will create a csv file which can be imported into MATLAB. If your mesh is too fine and if you don't need all the data, you can "Insert > Point Cloud" at the selected surface which the required point density and you can export this Point Cloud the same way as mentioned earlier.