Translation:I do not like anybody in parliament.
As is explained in the tips and notes, 'ki' can turn locatives into elements with an adjectival role. It is this alteration that allows 'mecliste' to modify (and therefore be directly applicable to) 'kimse'. Without 'ki', this connection would not exist and 'mecliste' would just be a plain old locative that could only be interpreted as referring to the subject.
I am not entirely sure my explanation will be correct but hopefully a native speaker will correct me in case it is wrong. As I see it, the adverbial phrase "in the parliament" modifies the pronoun "nobody". That's why it needs ki at the end. On the other hand, in your sentence okulda doesn't modify milk. Imagine asking about it, that might help. "We drink milk." "Where do you drink it?" "We drink milk at school." You are not talking about a specific kind of milk. But with the parliament, you cannot really ask "Where do you like nobody?" It doesn't make sense. The phrase "in the parliament" belongs to nobody, it means you don't like anybody that works in the parliament. I think that if you omitted ki, it would mean you don't like anybody in the whole world in general and then by mecliste you say that you find yourself in the parliament when you feel not liking anyone. When you drink school at milk, you probably drink normal milk and it happens when you are at school. It is not a special "school milk", you are talking about the activity of consuming something and where you do it. I thinik that if you said milk from a farm, it would have to be with ki, because it is a special kind of milk that is fresh and superhealthy etc. And that "nobody" is also from a special group, he is determined by his working in the parliament. I am not sure if I made myself clear... I hope it helped a bit :)
I can get a faint idea of 'ki' when I translate to Urdu, where the word wali is used, such as parliament wali, meaning those who are connected to the parliament. Another example of how I understand it is: In urdu it woukd be Militari wale koi bhi pasand nahi hai I don't like any military (type) or anyone having to do with the military.
Sadly my grammer is zero and to make up I search the five languages that i speak for similiar usage, all of which have influenced the turkish langiage or have been influenced. by Turkish But I could be wrong, here, way of the mark, so correct me