I've noticed myself getting skill points from completing certain quests and selling runes back to Ostegoth. Does anyone know the maximum amount of skill points you can get, and how you get them?
Leveling to 30 gives you 29 points.
Selling a rare artifact to Ostegoth gives 1 skill point as you said and there's 5 of those relics per playthrough. Since there are max. 2 playthroughs you can gain a total of 10 points this way.
Per playthrough there are 5 quests (I do not know which ones specifically) that grant you 1 skill point, which again gives a total of 10 points.
There are no other ways to get skill points which results in a total of 49 skill points.
Note: there are 33 skills each with 2 upgrades resulting in 99 total skill points needed, so it's impossible to max both the trees!
On your first playthrough max level is 22, so with some quests giving skill points and Khagoth relics giving 5 skill points (I also think you get skill point for finishing quest but I forgot tbh) all in all this all can net you 31 skill point max ^^ just finish all quests and you will have this ^^
On your next playthrough with same character you can go up to lvl 30 and probably collect relics again tho I'm not sure, I just finished game today and I done all quests so I'm starting new game+ now ^^