O&K Print Watch shows the paper size for my plotter as C-size sheet,D-size sheet etc. Can I view the sheet size in the ISO format A2, A1 etc?

O&K Print Watch uses the default system of units for displaying the size of paper or sheets. For displaying it in ISO format you should change the system of units to the metric one (Windows Control Panel->Regional Options->Numbers) on that print-server where O&K Print Watch is installed.