Welcome to this forum and to Dumaguete!
I researched the Duma area last month and here's what I found. After running a test at 4 locations using a phone and the Speedtest app, I found 3 of the 4 locations had greater than 20mpbs. My sole criterion for bothering to test the speed at their location was that they stated they had PLDT Fiber internet installed.
If you are in Duma and you need speeds of at least 10mpbs, the property must have PLDT Fiber. However, this isn't enough. You must also ask how many people share the line. In one case, a place had PLDT Fibr at 50mpbs but it was shared by 49 units, so night time rates would probably only average 2-5mpbs at best (what they told me).
I stayed at Hassaram court after calling them ahead of time. In addition to PLDT Fiber, they also had the new Google Wifi plan. Basically these are Google's version of old fashioned wifi repeaters. They work amazing and I was averaging 55mbps+ during my entire stay (see attachment).
I also visited a place called Honey Villas and they had over 45mbps and Google Wifi plan.
Finally, I visited Dumaguete studio apartments. They also have PLDT Fiber. I didn't test the speed of their internet but with a 5.0 Google rating across many reviews I believe their internet would be acceptable for a digital nomad (albeit with a monthly rental of $600!).
I also called Treetops B&B per DavyL200's recommendation. They also have PLDT fiber and not a lot of rental units so it's also reasonable there would be at least 20mpbs connection speed there.
Good luck and don't forget to go to Sans Rival for pastries early and often.