I personally found 9-hole challenges the easiest way of boosting gamernet points.
Sheshan is IMO the easiest course. Use the filter and pick 9-hole challenges that have 8 or 9 birdie runs plus maybe requiring a couple of eagles. The front 9 at sheshan is slightly more challenging than the back 9. Some holes are gimmee eagles (e.g. 2nd) so don't be put off if it requires a score of -11 or so.
Each of these is worth between 1600 and 2000pts if they've not been busted.
Long drives worth around 400pts are worth trying as well if your stats are up to it, the loading times are frustrating and they'll often get busted whilst you attempt them though.
Whichever method you choose, it's going to take a while to get to 50k!