[Went OT was thinking throwing knife not throwing goblin
For throwing knifes it isn't real hard with a full sized knife to throw it. Though tomahawks are a lot easier to throw. The first time my friend, who is into blackpowder & etc, showed me how to throw tomahawk I was able to make it stick on the second throw.
I think if one practiced once or twice a week throwing hawks or purpose built knifes you could have a combat level of skill in 6 months or so. Not saying you would be able to throw 100% in real world situation, but the truth of the matter is that 50% hit rate is good with handguns in real life.
I was a RO for a trail walk couple of years ago. And at a few of the stations the people had to throw their hawk and their partners hawk at a target. Only couple managed to stick their hawks but they had to throw at unknown range and deal with brush & etc.