I don't know your answer since I don't have that model. I realize that you are only asking for a simple measurement and not an explanation of the process.
However, there are numerous Youtube videos on setting up your WDS. The starting point is leveling up your trailer on a level surface and measuring the height of the bottom of the coupler. Try to get the trailer as level as possible, but close is probably good enough. No two people will arrive with the exact same measurement.