「君のことが好きだ」这里面的「こと」 是「事情」的意思，在句子中有强调之意！ 可以解释为「我喜欢你的一切」。 使用「君が好きだ」也可以，但「君のことが好きだ」会比「君が好きだ」感觉还要来的强烈 XD！

I'm not sure exactly,but In my opinion that こと is thing. For example. 君が好きだ = I love to you. 君のことが好きだ = I love for thing about you. I think こと include for everthing. If I say 君のことが好きだ,that means I don't love limited to just you,I love all things about you.which include your background,family,personality,figure and so on.that's everthing around you. Ofcouse you can say 君が好きだ,but 君のことが好きだ is more emotional expression.

if u said "こと"in this sentence, it would be emphasized that u love the "person". But if u didn't put "こと"in the sentence, it would mean just "u love a person." well, I mean that is just more emphasized. u can say"君が好きだ". meaning is pretty much same. :)

Wow tough question. Im not an expert but I will try and see if I can answer it. ~koto da (2kyuu bunpou form): = When you want to tell someone that something has importance Example: 大学に入りたければ、一生懸命勉強することだ。 So in this this sample, we add "koto" to tell the importance of studying in regards to if you want to enter the university. Kimi no koto ga suki da= I want to tell you the importance of how much I like "you". Kimi no koto is a way to tell the significance. I hope that helped! がんばってね。