The Air Traffic Control section on your Jeppesen has the information on CPDLC/ADS procedures for each air space including position report requirements. It will say something along the lines of "position reports are required regardless of ADS connection"(press send after passing the fix) or "position reports will be made primarily trough ADS" (don't send after passing the fix)
There are a few things to remember while operating with CPDLC, make your weather deviation requests early because sometimes it takes a little while for them to get back to you and make requests that won't need to be amended (if you think you need 10 miles right of track, request 15)
Don't amend the flight plan on the legs page, some folks like to place the boundaries for example for reference but this will send an ADS position report at that modified position to ATC (wether you send it or not) most controllers don't say anything but sometimes they do send a request for you to confirm your position just to make a point.