Well, we can see from the filters that he has, in the main (and biggest) skellige island, 7 caves to explore (probably some of them were already explored), 1 bounty monster, 3 bandit camps (I think), 6 contract quests(that he picked in the village), 3 dicks (or temples, or something), 2 treasures (or some kind of money, a bag icon can represent so many things), and roach of course
Probably except from caves and "temples" all the icons pobably disappear after completing the task (caves and temples still remain after you interact with everething possible there), perhaps the bandit camps respawn, and the icon remain
Well, remembering that geralt is level 35 so he had done already a lot, and that there are contracts from other cities (we can speculate that, since blandare, village he was, had 6 contract quests, that the other villages will have abour 4-6 too, well, from the image we can see fayrlund, a slighty bigger village that probably has 6 too,in the left sund, a plac with two houses so probably no contract, and more in the left a village with the name cutted because yes, with probably about 6 too, plus kaer trolde, which doesn't seem really big and has like, 8 quests. That makes 26 contract quests in the area that the image covers).
26 contract quests that can be anything, plus probably 4-6 monster bounty quest and 6-8 bandit camps ard skellige (or part of it) already has 36-40 quests to do
This speculation of mine is really inacurate but we can expect a number like that from ard skellige the biggest island of skellige island, plus no mans land/novigrad that make a kinda big number