I don't underatand why "iku no ga suki" uses two particles in one place. I don't think I've seen this before.
You can have multiple particles. Theの here is marking the verb a noun, and the が is marking our now noun/gerund "going" as the subject.
I think GA makes it an object in this case.
a person or thing to which a specified action or feeling is directed.
Also grammatically correct?
I always seem to have trouble figuring out when it's 行く or 行き. And other similar verbs.
行く is the regular version non-keigo. If it stands alone it just means "going". 行き can only be part of 行きます or 行きました/行きたい and so on. 行き on it's own is not used.
There is a KA instead of GA.
There are both because you need both.